ELECTRIC LIGHT APPLIED TO MICROSCOPICAL RESEARCH, 145 

accumulators. ‘This bluish light is well suited to the experiments 
of photo-micrography, but is too vivid for ordinary work. The 
chief incandescent lamps in vacuo are those of Edison and Swan. 
Those of Maxim are incandescent in a rarified hydro-carbon. We 
have tried those of Maxim, but the Swan lamps are the ones we use 
‘daily. These suit the micrographer better than any other, both 
because their incandescent filaments are united upon a small space, 
and also because they can be made to work with much less force 
than the Maxim lamps. Some weeks ago we received from the 
Newcastle electrician some special small lamps eminently suited for 
micrographical research, and now we employ these alone. These 
small lamps are almost spherical and about three centimetres in 
diameter. They give a vivid light and require but a small force. 
To obtain a beautiful white light it is only necessary to connect 
with it from six to eight Tommasi cells, or four Faure-Reynier 
accumulators. 
The micrographer therefore can provide for all his researches by 
means of ten ‘Tommasi cells or four accumulators, 
These accumulators are easily charged by the aid of the ten 
‘Tommasi cells (these first having only an electro-motive force of 
8.5 volts, while the ten Tommasi have 18 volts), and as these four 
accumulators, according to our experience, will supply the small 
lamp for more than twelve hours, we may have the electric light 
‘continually at our disposition by setting the pile in operation once 
or twice a week. 
APPLICATION OF THE ELECTRIC LIGHT TO THE MICROSCOPE. 
Let us see now what the micrographer will desire from the use 
of the electric light. These advantages are of two kinds: 
IV. ILLUMINATION OF THE MICROSCOPE. 
The incandescent electric light surpasses all other illumination, 
It has the softness of good rock oil lamps, and shews up fine 
details almost as well as the mono-chromatic light. The delicate 
strie of Amphipleura, the roth band of Nobert’s test can be seen 
with perfect distinctness. Prof. Abbé, to whom we have communi- 
cated the result of our researches, finds a theoretical explanation 
or it. He attributes it to two causes : 
1. The great whiteness of the light. Consequently the light 
contains more blue and violet rays. Now, as it has been proved 
by measurements made by Prof. Abbé, in different mono-chromatic 
illuminations, that the resolving power of an objective of given 
aperture increases in the same ratio that the length of the wave of 
light decreases, it follows that the electric light must shew fine 
details more easily than the yellowish light of gas or lamps. 
