141 
various bodies lo the Chemical Rays. 
using the galvanometer at the same time to mark the intensity 
of light, try every substance under precisely the same circum- 
stances. Having completed the exposure of a series, I place 
all the discs in the mercurial vapour-box together, and the 
instant the impression appears the strongest, remove them and 
carefully compare effects. 
The following are the results I have arrived at by these 
means. At the head of each series I have placed the mean 
permanent deflection of the galvanometer needle, from ten 
careful experiments with each of the bodies included within 
it. By this means a comparative view is given of one series 
with another. ^ 
Series 1 . — Defection 22° 30". 
Nitrogen 
Atmospheric air 
Oxygen 
Hydrogen 
Carbonic Acid 
Carbonic Oxide 
Steam (invisible) 
Nitrous Oxide 
Water 
Alcohol (absolute) 
>®ther (sulphuric) 
Series 2. — Defection 20°. 
British Plate Glass 
Iceland Spar 
Carbonate of Soda 
Nitrate of Potassa 
fused and opake 
Camphor 
Sulphuric Acid 
Hydrocyanic Acid(Scheele’s) 
Nitric Acid 
Series 3. — Defection 18° 80". 
Crown Glass 
Flint Glass 
Mica 
French Plate Glass 
Alum 
Gum Arabic 
B. Plate and Crown Glass 
German Plate (with a pink 
shade) 
Two pieces of Crown Glass 
Purple Fluor Spar 
Nitrous Acid Gas 
Iodine Vapour 
Series 4. — Defection 17° 15'^, 
B. Plate and Flint Glass 
Flint and Crown Glass 
Three pieces of Crown Glass 
Three laminae of Mica 
Creosote 
Oil of Aniseed (German) 
Peppermint (English) 
Rosemary 
Savine 
Four pieces of Crown Glass 
Amber 
Green Fluor Spar 
Oil of Lavender 
Caraways 
Cloves 
Canada Balsam 
Series 5. — Defect io7i 4° 35". 
Green Bottle Glass* 
Chlorine 
Protoxide of Chlorine 
Bromine (vapour) 
■ (liquid) 
Lightly-smoked Glass 
* I have been much surprised at some of the manufacturing chemists 
in London sending out their hydrocyanic acid and other easily decompo- 
sable preparations in bottles oi purple glass, which offers no interruption to 
the chemical rays. Dark green glass should be substituted. 
