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Proceedings of the Royal Society 
of the prism box. If it becomes too warm in the box, the reverse 
action takes place ; the current is broken, and the heat is shut off. 
J ust before my brother’s death, it was decided to make a slight 
change in the heating part of the apparatus, because on one occasion, 
as we were watching it, we found that the sudden action of the 
electro-magnet on the valve of the gas lamp in shutting off the heat 
had caused the light to become extinguished. On the cooling of 
the inside of the box the electro-magnet opened the valve, and 
allowed the gas to escape into the room, making it very dangerous. 
It was then decided to change this portion of the apparatus. It was 
thought that it would be safer to have the electro-magnet control a 
damper in the hot air pipe, than the lever of the gas lamp 
It was also decided to have the hot air pipe in the prism box 
make several turns around its inside, so as to dispense with the 
double box and cotton filling, and have a more even distribution of 
heat throughout the box. 
What you so kindly say of my brother’s early death is too pain- 
fully true. It awakens reminiscences that cannot, and should not 
be forgotten. If some twenty years ago you could have looked into 
the laboratory at Hastings, you would have witnessed the interesting 
sight of my father John "William Draper, and his three sons all dis- 
cussing together the best plan to be followed in the building of my 
brother Henry’s observatory, and then after its construction father 
would often leave his work on the Intellectual Development of Europe , 
and go to the observatory to deliberate what observations should be 
made, and how they should be carried on, Father was a born 
astronomer, scientist, and historian. When only eight years of age 
he attempted to make a Gregorian telescope like the one he saw his 
father using. 
But how strange is death. Brother Henry, in the prime of life, 
followed father to the grave in ten short months. — I am, very truly 
yours, Daniel Draper. 
