and Polarization of Heat. 133 
Loni has described, in his paper in the Annales de Chimie for May 
1833, a simple and satisfactory method of estimating the relative 
values of degrees, at different points of the scale. He states, 
however, that, under 20° of deviation, he found them quite uni- 
form. In the following experiments, the deviations were gene- 
rally under 15°, and in almost no case exceeded 20°. I have 
therefore assumed the forces to be as the deviations. Besides, 
no change of importance would take place from a deviation from 
this law by a small quantity. 
5. It will be perceived in the experiments which are to be 
detailed, that the determination of all the more important facts 
depends generally on whether one effect be greater or less than 
another, without much regard to their absolute amount. Now, 
the confidence which we can place in the uniformity of this in- 
strument, or at least of the small changes capable of affecting it 
(since it is not liable like thermometers, and especially air-ther- 
mometers, to advance by starts) is such, as to admit of almost in- 
definite subdivision, where the relations of small quantities are 
alone concerned. I conceived, therefore, that, without impairing 
its sensibility by lengthening the galvanometer needle, we might 
advantageously magnify the divisions by optical means. This I 
proposed to do by observing the motions of the index by means 
of a small telescope, fixing im front of the object glass a lens whose 
focus is situated at the part of the scale desired to be magnified. 
It might also be easy, in order to compare larger quantities, to 
make this micrometric system revolve so as to be always similarly 
placed as regards the needle, and thus avoid the effects of paral- 
lax, which at present require constant vigilance. 
6. The method here indicated, I have put in practice with 
the greatest success in my later researches ; one-tenth of a degree 
becomes easily visible, and the constancy of the indications fully 
justify this method of microscopic examination, which has enabled 
me to verify the most delicate deductions I had drawn from 
