OF ARTS AND SCIENCES. 245 



well as light the dark rcom ; and also tliat it can be used in the even- 

 ing and on dark winter afternoons when daylight is out of the question. 

 Moreover, since the gas-flame is much more uniform in brilliancy, it is 

 correspondingly easier to determine when a plate is properly developed, 

 and fewer plates are lost in this way. 



Experiments with the following media have been made, and are 

 numbered in the second and third columns in the order of their de- 

 sirability. It will be noticed that there are five media which with 

 gas-light give better results, i. e. less fog, than the best medium with 

 daylight. In the second series the third column gives the distance in 

 inches in each case at which the fine details were visible from the gas- 

 flame. No medium is wholly satisfactory with daylight unless it 

 contains red glass or paper. The window used with the gas-light 

 measured six by seven inches, and was situated fourteen inches from 

 the gas-flame. The window used with daylight measured five by five 

 inches. Direct light from the clouds was used. The plate was de- 

 veloped in the first series with oxalate, and in the second with pyro and 

 soda develoj^er. 



First Series. 



Colored Media. Gas. Sky. 



Reel and yellow glass 1 12 



Red and ground glass 2 6 



Post-office paper 3 14 



Red glass 4 8 



Yellow glass double 5 16 



Yellow and violet glass 7 18 



Carbutt's red paper 9 10 



Red glass double 11 13 



Yellow and green glass 15 17 



Second Series. 



Colored Media. Gas . Indies. 



Canary paper double 1 8 



Golden fabric double 2 29 



Red glass 3 38 



Golden fabric single 4 58 



Rod, yellow, and ground glass 5 11 



Red and yellow glass C 22 



Canary paper single 7 19 



Post-office paper 8 lo 



Yellow and green glass 9 41 



It was found that ground glass transmitted fifty-five per cent of the 

 lio^ht from a gas-flame coming through red glass, while it transmitted 



