So I've read up a little bit on Langley's bolometer, a device made in the 19th century using two strips of platinum and a galvanometer. From what I can gather, a galvanometer works because the temperature of one of the strips changes in response to incoming photons (or other particles), and this alters the resistance... which alters the current from an applied voltage. First of all am I correct (please tell me if I've got anything wrong)? Second of all, I'm aware Langley used this stuff for astronomy and long-range measurements, is the resistance of platinum really that sensitive to incoming radiation over such a huge distance? What is the property associated with this? I also did some looking but could not find any values, how sensitive (to current) is the galvanometer used?