EDIT: Found it again https://en.wikipedia.org/wiki/Campbell%E2%80%93Stokes_record...
You can see the tracks of the days and the cloud cover in those photographs. Note that the multiple year ones have multiple days going over a single track.
Aside from the extreme reciprocity failure in the film, its "only" about three stops from a one day exposure to a one week exposure... and another two stops to a month, and then another three and a half stops to a year.
The correction for a 1200 second (20m) exposure on Kodak black and white film was at 12x (for 14400s, 4h). However, the extrapolation for the curve for Provia 100F put the reciprocity failure for 1200s at 2.35 for a 3000 second exposure.
Looking at the methods and results is interesting, though I've gone nearly full digital now.
I keep looking at it, my brain confused why I can't see through what is clearly a transparent object. It doesn't feel like I'm looking through it, though inverted; it feels like I'm seeing a weird depiction of the nature scene around me plastered on its surface.
https://www.treehugger.com/solar-technology/solar-prototype-...
https://cleantechnica.com/2013/12/23/solar-ball-lens-improve...
Not solid glass, though (I don't know what it is, but I imagine there's an upper limit on size of solid glass spheres that can be made)...
> This isn't the first time Viñoly's architecture has raised eyebrows as well as temperatures: His Vdara Hotel in Las Vegas has been criticized for directing sunbeams onto the swimming pool deck that are hot enough to melt plastic and singe people's hair. The hotspot became known as the "Vdara death ray."
Based on this I'm inclined to believe Viñoly fits the negative "rockstar architect" stereotype. I mean, making that mistake once is one thing, but then doing it again?
Actually, https://en.wikipedia.org/wiki/Solar_furnace ... The furnace in Odeillo, France can reach up to 3500 °C, and it's cross section is just about 50x50 meters. Of course, your typical skyscraper won't create those temperatures accidentially, but if you have the surface area of a skyscraper side in mirrors and can arrange them like you want... it gets pretty pretty hot.
That's the temperature, about the energy: Steel melts at 1370 °C, specific heat of carbon steel is 490 J/kg K. I can't find the actually melting energy. But this means, roughly, that you need 168.5 kWh to raise a ton of steel to melting temperature. The Wikipedia article says the Odeillo device creates 3200 kW (although that paragraph seems to be cut off)., so in principle it should be possible to melt a car. Scary thing.
Big table-top loupes for fine electronics work are similar fire hazards. Ours now all have shutters and big warnings that the shutter must be closed when not in use.
Hours later as we were eating lunch the sun struck the mirror at just the right angle, and as we look over at the parking lot there's smoke billowing out of the car. Luckily there was no fire, but there was a line burned across the underside of the dashboard. It looked like someone had taken an acetylene torch to it.
Also, people can't apply what they were supposed to learn in high school physics. It's not only Brazil that has this problem:
Well, it's very rare and therefore you don't think about it.
I make telescope mirrors, so I can't be accused of being unaware of the laws of optics. Yet until now I never thought about crystal balls (heck, even acrylic balls) as a potential fire hazard inside the house.
Approximately spherical transparent objects are common. Approximately cylindrical and spherical reflective surfaces are common. Situations where you can apply high school physics are very, very common. Most of us just don't, because we're not trained to do so. We're trained to do the homework problems and answer the test questions. But don't we learn this stuff so we can use the knowledge in life?
I can't be accused of being unaware of the laws of optics. Yet until now I never thought about crystal balls (heck, even acrylic balls) as a potential fire hazard
So you're over halfway there. Now we collectively have a chance to learn the meta-lesson about applying knowledge.
Also clear water bottles (filled with water). In 1991 there was a brief period where homeowners all over Japan were putting clear PET bottles (PolyEthylene Terephthalate) at the edge of their properties because it was asserted on some talk show that the sparkles would keep animals away. This ended abruptly when a series of fires were started by the bottles.
Supposedly it confuses flies and they'll leave the area alone. I've never seen any evidence of this.
Every once in a while a house fire is started because the sun sat at just the right angle at a certain time of the year, placing the focal point on the curtains. But because the risk is so low (it doesn't happen that frequently) many people are completely unaware of the phenomenon.