The observatory had been abandoned for 3 years when Evelyn Grant first saw it in October 1897, built in 1891 by a mining company to survey their claims and predict weather patterns. The structure had been left empty when the mines closed and the company dissolved. The building sat on a hilltop 5 miles from Helena, Montana territory.
a circular stone tower 20 feet in diameter with walls 2 feet thick and a domed roof made from copper sheets. Evelyn had been looking for cheap housing and abandoned counted as cheap. She was 34 years old, a widow supporting herself through clerical work at the territorial land office. Her husband had died two years earlier in a mining accident, leaving her with no property and minimal savings.
Rent in Helena consumed half her wages, leaving little for anything else. When she’d heard about the abandoned observatory from a surveyor filing mineral claims, she’d asked who owned it. He’d told her probably nobody. The mining company had never filed proper title, and the structure sat on what was likely public land.
She’d ridden out to see it the next day. The observatory was remarkable architecture for its purpose. The stone walls were constructed from local granite, fitted carefully and mortared solidly. The circular design eliminated corners where heat could be lost and provided maximum strength against wind. The copper dome roof, though weathered green with age, showed no signs of leaking.
Most impressively, the walls were filled construction, meaning the twoft thickness wasn’t just stacked stone, but included rubble and mortar filled between inner and outer stone faces. This created thermal mass that would moderate temperature dramatically. The interior was a single circular room approximately 300 square ft. A spiral staircase of iron led up to an observation platform beneath the dome.
The original telescope mounting remained. A heavy iron framework bolted to the floor, though the telescope itself had been removed when the observatory closed. Windows were small and positioned high, designed to minimize light interference for astronomical observation rather than for residential comfort.
The floor was stone, the walls bare granite, and the space had no heating system beyond what the mining company had used, which appeared to have been small portable stoves long since removed. Evelyn’s first task was establishing whether she could legally occupy the structure. She’d researched at the land office where she worked, finding no recorded deed for the hilltop parcel.
The mining company had operated under federal mineral claim, which didn’t include surface rights to structures. She’d filed a homestead claim on the quarter section that included the observatory, paying her $14 filing fee and committing to the required improvements and residence. The land office clerk had looked puzzled when she described improving an existing stone observatory, but the claim was legal, and he’d processed it.
Her second task was making the space livable. The observatory had been designed for occasional use by surveyors, not for residential occupation. She needed to add a door, as the original entrance had only a temporary wooden panel. She needed to partition part of the space for privacy. She needed to install a proper heating system, and she needed to do all this before Montana winter arrived in earnest, which gave her perhaps 6 weeks.
The door she’d purchased in Helena, a solid oak door with frame, hauling it to the hilltop on a rented wagon. Installing it required drilling into the stone archway. Tedious work with a star drill and hammer. She’d spend 3 days creating holes deep enough to anchor the frame securely. The door, once installed, sealed the entrance, effectively transforming the observatory from an open structure to an enclosed space.
For privacy, she’d hung heavy canvas curtains on a wire suspended across the room, creating separate areas for sleeping and living. This was temporary, but canvas was cheap and effective. Eventually, she’d build a proper interior wall, but canvas would suffice through her first winter. She’d also added rugs purchased from a secondhand dealer, covering the cold stone floor and making the space more comfortable.
The heating system became her focus because it was essential for survival and because the observatory’s design offered unique opportunities. The 2-ft thick stone walls were enormous thermal mass, equivalent to perhaps 40 tons of granite. If she could heat this mass, it would radiate warmth for extended periods, requiring far less fuel than heating air in a thinwalled cabin.
But heating that much stone would require a different approach than conventional cabin heating. She’d purchased a large cast iron stove, the biggest she could afford, and positioned it at the room’s center. This central placement meant heat would radiate in all directions, warming the circular walls evenly. The stove pipe rose straight up through a hole she’d cut in the copper dome, exiting at the peak.
This vertical rise created excellent draft and minimized heat loss through the stove pipe path. She’d sealed around the pipe with fireresistant mortar and copper flashing, ensuring weather tightness while allowing for thermal expansion. Her innovation was adding thermal storage beyond just the walls. She’d gathered field stones and built a ring around the stove’s base, creating a stone collar roughly 4 feet in diameter and 2 ft high.
This stone mass would absorb heat directly from the stove, storing it and releasing it gradually, combined with the walls absorbing radiated heat from the stove and the stone floor beneath conducting heat downward into its mass. She’d created a thermal battery far larger than any conventional cabin possessed. The first serious cold arrived in late November.
Outside temperatures dropped to 10° and Evelyn lit her first substantial fire in the observatory stove. The building’s response was slow but dramatic. The first day, interior temperature rose from 35° to 50° despite the massive stone mass absorbing heat. The second day, with continued moderate fire, temperature reached 60°.
By the third day, the stone walls had absorbed enough heat that they felt warm to the touch, and interior temperature stabilized around 65°. What surprised Evelyn was how little fuel this required once the thermal mass was heated. After 3 days of moderate continuous fire, she could let the fire die at night, and the temperature would only drop 3 or 4° by morning.
The stone walls, having absorbed heat for days, released it slowly through the night. A small morning fire would restore temperature and continue charging the thermal mass. She was burning perhaps one quarter the firewood she’d burned in her previous rented cabin. Her first visitor was a neighbor named Robert Chen, who homesteaded 3 mi away.
He’d seen smoke from the observatory and had ridden over to investigate, who was living in the old survey building. What he found amazed him. The observatory interior was warmer than his cabin, despite Evelyn’s fire being relatively small. He’d felt the stone walls, impressed by their retained heat. He’d asked how this was possible, and Evelyn had explained thermal mass and the advantages of massive stone construction.
Word spread quickly through the Helena area. The widow living in the old observatory had somehow made it the warmest dwelling in the territory. People started visiting curious about the unusual residence and its heating performance. Evelyn would show them the thick walls. Explain how stone absorbed and stored heat. Demonstrate how the circular design eliminated cold corners.
Most visitors were skeptical initially, expecting the stone building to be cold like a cellar. Finding it warm and comfortable, challenged their assumptions about what made good housing. The territorial surveyor, who’ originally told Evelyn about the observatory, came by in January during a cold snap that had dropped temperatures to 30 below zero.
He found her comfortable in the circular stone room. Temperature perhaps 55°, wearing normal indoor clothing rather than the heavy layers people wore in conventional cabins during such cold. He examined her stove, her firewood consumption, and her temperature records. His professional assessment was that the observatory’s thermal mass created heating efficiency impossible to achieve in conventional woodframe construction.
Evelyn’s daily routine adapted to the building’s characteristics. She’d maintain a small fire through the day, enough to keep the stove and its surrounding stone collar hot. This charged the thermal mass continuously without overheating the space. At night, she’d bank the fire, reducing it to coals that would burn slowly until morning.
The thermal mass would maintain comfortable temperature through the night. Morning, she’d revive the fire and continue the cycle. This routine required far less attention than conventional heating, which needed constant fire tending to prevent temperature drops. The stone floor presented challenges she’d had to address.
Stone conducts heat well, which meant the floor absorbed warmth and could potentially drain heat from the space. She’d addressed this by covering the floor with layers of rugs and in her sleeping area, building a raised wooden platform that created an insulating air gap. The floor’s thermal mass was actually beneficial once heated, radiating warmth upward, but it required careful management to prevent it from acting as a heat sink.
The high windows, initially seeming like a disadvantage, proved beneficial for heating. Small windows meant minimal heat loss through glass. The weakest point in any building envelope. The high position meant winter sun. Low on the horizon would shine deep into the space, providing solar gain. She’d cleaned the windows thoroughly, removing years of accumulated dirt, and found that winter sun contributed measurably to daytime heating, reducing her fire requirements.
The copper dome roof had concerned her initially. Metal conducts heat readily, suggesting the dome would lose warmth rapidly. In practice, the dome’s double curve created an airspace beneath it where hot air accumulated. This hot air layer insulated the dome from inside, preventing rapid heat loss. The dome’s weathered copper surface also reflected solar radiation in summer, a benefit she’d appreciate later, but which was irrelevant during winter.
By February, she’d refined her heating system further. She’d added more stone mass around her stove, expanding the heated collar. She’d also begun experimenting with fire timing, learning that one large fire that heated the mass significantly was more efficient than multiple small fires. She developed a routine of building a substantial fire each evening, heating the stone mass thoroughly, then maintaining minimal fire overnight and through the next day.
This weekly thermal recharge proved sufficient to maintain comfort. The observatory’s hilltop location, initially seeming like an exposure problem, actually provided advantages. The elevation caught more winter sun than valley locations. The exposure to wind was mitigated by the circular stone walls strength and the absence of corners where wind pressure could concentrate.
The hilltop position also meant cold air drainage with the coldest air sinking into valleys while the observatory sat above it. On calm cold nights, the temperature at the observatory could be 10° warmer than in Helena proper simply due to elevation and cold air pooling. Her transformation of the observatory attracted attention beyond casual visitors.
A professor from the Montana School of Minds came to study the heating system. Interested in practical applications of thermal mass principles, he’d measured temperatures at various points in the walls, finding that the inner surface stayed perhaps 60° while the outer surface might be only 20°, demonstrating the insulating effect of the massive wall thickness.
His students wrote papers about the observatory as an example of passive thermal design. A wealthy Helina resident offered to purchase the property from Evelyn, wanting to use the observatory as a retreat. Evelyn had declined, both because she’d filed homestead claim and had no intention of abandoning it, and because selling would leave her back in expensive rental housing.
The observatory was hers through occupation and improvement, and it provided housing quality she couldn’t afford to purchase elsewhere. She’d stay. She’d lived in the observatory through five winters from 1897 to 1902. During that time, she’d continued improving the space. She’d built proper interior partitions from lumber, creating separate bedroom and living areas.
She’d installed a hand pump and sistn, collecting roof runoff for water supply. She’d added shelving and storage using the natural recesses in the stone walls. She’d painted the interior walls white, dramatically improving light levels and making the space feel larger. The observatory had evolved from abandoned survey station to comfortable, efficient home.
In 1902, she’d remarried, wetting a mining engineer named James Morrison, who’d been one of her frequent visitors. Initially curious about her heating system, but eventually interested in Evelyn herself. They’d continued living in the observatory, James appreciating the building’s efficiency and unique character. They’d built a small frame addition for additional living space, but the original stone tower remained their primary residence and their heating core.
The addition was kept warm by heat migrating from the observatory proper, requiring no separate heating system. By 1920, the observatory had been residential for 23 years and had become locally famous as an example of adaptive reuse and efficient design. Architects from Denver and San Francisco visited to study the conversion, documenting how Evelyn had transformed survey equipment housing into comfortable residence.
Several similar conversions were attempted with other abandoned industrial structures, though few achieved the observatories heating efficiency because few had comparable thermal mass. The buildings stood through the 1950s, still occupied and still heated primarily by the thermal mass system Evelyn had developed.
Eventually, it was designated a historical landmark preserved as an example of frontier resourcefulness and early understanding of passive solar and thermal mass principles. Modern earth sheltered and highmass homes use the same concepts Evelyn had employed from necessity, though now with engineering analysis and computer modeling rather than observation and experimentation.
The lesson the observatory taught was about looking beyond a structures original purpose to see its potential for adaptation. Most people had seen an abandoned survey building useless for its original function and therefore worthless. Evelyn had seen thick stone walls, circular thermal efficiency, and a dome roof that could be adapted to residential use.
She’d recognized that the features making it good for astronomical observation. Massive stable structure and minimal windows also made it potentially excellent for efficient residential heating. Sometimes the best housing isn’t what’s conventionally built for that purpose, but what can be adapted from structures built for entirely different reasons.
The mining company’s decision to build with stone rather than wood had been driven by their need for stability. Astronomical observations required a platform that wouldn’t shift or vibrate. Wooden structures flex with temperature changes and wind pressure. Stone provides the rigidity necessary for precision instruments.
This same rigidity that benefited telescopes would benefit thermal performance as the stone mass wouldn’t expand and contract creating air gaps and drafts common in wood construction. The circular floor plan had been chosen for structural efficiency. A circle encloses maximum area with minimum perimeter reducing material costs.
More importantly, for an observatory, circular structure eliminates corners that could catch wind and create vibration. For residential heating, the circular plan meant heat from a central source would spread equally in all directions, warming the space uniformly without creating cold spots in corners. The geometry that served astronomy served heating equally well.
The twoft wall thickness had been engineering overkill for the observatory’s original purpose. The structure only needed to support a relatively light copper dome and resist Montana wind. But the mining company had built with available stonemasons who’ constructed mine buildings, and they’d built two mining standards, massive and permanent.
This overbuilt quality meant the observatory was far more substantial than residential construction required, giving Evelyn thermal mass she’d never achieved building from scratch. The granite selection had been pragmatic using stone quarried locally from the same deposits the mining company was exploiting. Granite is dense, approximately 165 lb per cubic foot.
The observatory walls contained roughly 40 tons of granite, creating thermal mass that would take days to heat fully, but would release stored heat over equally long periods. This slow thermal response was disadvantageous for the mining company’s occasional use, but was perfect for residential occupation, where temperature stability mattered more than rapid heating.
The copper dome’s construction had been sophisticated using techniques developed for industrial applications. The copper sheets were formed over wooden frames, then soldered at the seams to create a weatherproof shell. The dome’s double curve rising to a central peak created inherent structural strength without requiring internal support beyond the perimeter walls.
This self-supporting nature meant no interior columns interrupted the floor space, giving Evelyn full use of the circular room without structural obstacles. Her door installation had required adapting to stone construction techniques unfamiliar to most carpenters. Drilling into granite with hand tools was slow work. the star drill advancing perhaps an inch per hour of steady pounding.
She’d needed holes roughly 8 in deep to anchor the door frame securely. Eight holes meant perhaps 60 hours of drilling spread over 3 days of exhausting work. But once installed, the door was anchored as permanently as the walls themselves, creating a entrance that would last decades. The canvas partition system had been inspired by hospital ward dividers she’d seen in Helena.
Heavy canvas hung on wire could create visual privacy while allowing air circulation and heat movement. She’d purchased canvas from a tent maker. Selecting 12 oz duck canvas that would hang straight and block visual passage effectively. The wire suspension allowed easy repositioning if she wanted to reconfigure the space.
Eventually, she’d replace the canvas with built walls, but for her first winter, the canvas provided adequate privacy while maintaining the heating efficiency of one unified space. The rug layering on the stone floor had required understanding heat transfer through different materials. Stone conducts heat readily.
approximately 10 times better than wood. Without floor covering, standing on the stone floor would draw heat from her feet faster than her body could produce it, making the floor feel uncomfortably cold, even when the space was warm. Rugs created insulating layers that slowed this heat transfer. She’d layered multiple rugs in hightra areas, creating perhaps an inch of insulating material that made standing on the floor comfortable.
Her stove selection had been critical. She’d needed large firebox capacity to heat the massive thermal mass, but also good efficiency to avoid wasting fuel. She’d purchased a Acme Oakno 8 no, a large parlor stove weighing perhaps 300 lb with a firebox that could hold a day’s worth of wood if loaded properly. The stove cost $40, a significant portion of her savings, but it was sized appropriately for her heating challenge.
Smaller stoves would have taken weeks to heat the stone mass adequately. The stove pipe installation through the copper dome had required careful waterproofing. She’d cut a 10-in hole through the copper at the dome’s peak, the highest point where water would naturally run away from the penetration. She’d fabricated a copper collar that fitted around the stove pipe, soldering it to the dome surface.
This created a weatherproof seal while allowing the stove pipe to expand and contract with temperature changes without binding. The vertical rise of 30 ft from stove to dome peak created strong draft, ensuring complete combustion and efficient heat transfer. The stone collar around her stove base had been built using fieldstones gathered from around the hilltop.
She’d selected flat stones that could be stacked stably, building a circular wall that rose 2 ft high. The interior was filled with smaller rocks and sand, creating solid mass that would absorb heat from the stove’s radiant surface. This collar weighed perhaps 800 lb, far smaller than the wall mass, but positioned where it received maximum heat from the stove.
It served as immediate thermal storage that could release heat quickly into the room. Her first winter’s heating learning curve had been steep. Initially, she tried to heat the observatory like a conventional cabin, building fires when cold and letting them die when warm. This approach had been inefficient with the massive stone mass.
The stone would begin warming. Then she’d let the fire die and the stone would cool again before fully heated. She’d realized she needed sustained heating to charge the thermal mass then minimal heating to maintain it. This counterintuitive approach, heating continuously rather than intermittently, proved far more fuelefficient once she understood the thermal mass dynamics.
Her temperature records, kept meticulously through five winters, showed patterns that validated her heating approach. The observatory’s interior temperature would lag outside temperature by roughly 3 days. When a cold front arrived, outside temperature might drop 20° overnight, but interior temperature would drop only 2° overnight and would continue dropping gradually for 3 days before stabilizing.
When weather warmed, the interior would remain cool for days before gradually warming. This thermal lag meant she experienced far less temperature variation than people in conventional cabins. creating more comfortable living conditions. The firewood consumption measurements proved the systems efficiency quantitatively.
Her neighbor, Robert Chen, kept careful records of his wood use, burning roughly one cord per month through the winter heating season. Evelyn burned approximately one cord per 4 months, a quarter of his consumption for comparable interior temperatures. The difference was entirely attributable to thermal mass.
Her stove’s heat charged the stone mass, which released it gradually. His stove’s heatwarmed air that escaped rapidly through the thinner walls and ceiling of his conventional cabin. Her water supply system had required innovation beyond simple collection. The copper dome provided excellent roof catchment, shedding water efficiently to a gutter she’d installed around the perimeter.
But winter freezing meant she couldn’t store water in external tanks. She’d built an interior sistn beneath the floor, excavating a pit in the hilltop granite and lining it with stone and mortar. This sistern held approximately 300 g, enough for several weeks. Being below floor level and inside the heated space, it remained unfrozen through winter.
A hand pump brought water up for use. The lighting challenges of the small high windows had required multiple solutions. Winter days were short at Montana’s latitude, and the observatory’s windows admitted minimal light, even at midday. She’d painted the interior walls white, as mentioned, dramatically improving light reflection.
She’d also invested in good oil lamps, purchasing three highquality lamps that produced bright light without excessive smoke. The combination of white walls and efficient lamps made the interior adequately lit for reading and work despite the minimal natural light. The acoustic properties of the circular stone room had been unexpected.
The smooth stone walls reflected sound, creating echoes that made conversation slightly strange initially. She’d addressed this partly through the rugs and canvas partitions which absorbed some sound. She’d also hung heavy curtains on the walls in her sleeping area, creating sound dampening that made that section of the room quiet for sleep.
The stone walls did provide excellent sound insulation from outside, blocking wind noise and creating peaceful quiet that people in wooden cabins never experienced. The astronomical equipment mounting points in the floor had been repurposed creatively. The massive iron framework that had held the telescope was bolted through the floor into the granite bedrock below.
Evelyn had used these anchor points for various purposes, securing her bed frame, anchoring shelving, and even hanging her canvas partitions from overhead points. The mining company had installed permanence that served her needs perfectly, demonstrating how robust industrial construction could adapt to entirely different uses.
Her relationship with James Morrison had developed gradually through his repeated visits to study the observatory’s heating system. He’d been skeptical initially that stone construction could be warm, but multiple visits during winter had convinced him of the thermal mass advantages. Their conversations had ranged from heating engineering to mining geology to personal experiences, and friendship had evolved into romance.
When he proposed, they’d both agreed the observatory would remain their primary residence, both for its efficiency and for its unique character that neither wanted to abandon. The frame addition they’d built after marriage had been positioned on the south side, maximizing solar gain. It was connected to the observatory through a doorway cut into the stone wall, a major undertaking requiring weeks of careful stone cutting.
The addition provided space for a kitchen and additional bedroom, but it was heated entirely by warmth. migrating from the observatory main room. They’d installed a small stove in the addition for supplemental heating on extremely cold days, but normally the thermal mass of the observatory warmed the addition sufficiently.
The long-term durability of the stone structure impressed everyone who studied it. By 1920, 30 years after construction, the observatory showed minimal wear. Stone didn’t rot like wood, didn’t rust like metal, didn’t deteriorate like adobe. The copper dome had aged gracefully. Its green patina protecting the metal beneath.
The only maintenance required had been occasional mortar joint repointing where weathering had eroded surface mortar. This minimal maintenance meant the structures total cost of ownership was dramatically lower than wooden buildings that required constant repair and eventual replacement. The historical preservation in later decades recognized the observatory as significant both architecturally and socially.
Architecturally, it demonstrated adaptive reuse decades before that concept became common in urban planning. Socially, it represented frontier resourcefulness. The willingness to see potential in abandoned structures and to apply engineering principles towards survival. Evelyn’s heating system became a case study in passive solar design and thermal mass applications.
cited in textbooks and academic papers long after her death.
