88 A. UM. Mayer—Boundary of a Wave of Conducted Heat. 
Exp. Major Axis. Minor Axis. Ratios. 
] 12°50 9°75 1°28 
% 11°60 8°50 1°35 
3 10°00 7°50 1°33 
4 12°00 9°00 1°33 
5 13°75 10°00 1°37 
6 18°00 14°00 1°29 
7 15°00 12°00 1°25 
8 9°75 7°50 1°30 
1°31 Mean Ratio. 
Sénarmont, in the above experiments, used every precaution 
to attain accurate results. He screened the plate from draughts 
of air and from radiations; kept the plate horizontal and_fre- 
ee. rotated it around its heated wire. After the ellipse 
had become constant in its form, he allowed the plate to cool, 
and then measured the axes of the ellipse by means of a 
micrometer. 
In the experiments which follow, I used a quartz: plate 
27™" long, 22™™ wide, and whose thickness was 1:2™™. Its 
center of figure was pierced by a hole 1:°25™™ in diameter, 
through which nied the <ainionl conical end of a silver 
wire. The iodide was made oa a paint with weak gum 
water, and in aa 1; 2, abd 4 was applied to the 
surface of the te by a camel's fait pencil. In experiments 
5, 6, 7 and 8, the fotics plan was adopted of flowing the iodide 
over the plate, and allowing the water spontaneously 
to evaporate. Thus we obtain a smooth, evenly distributed 
coating, erilg a sharp outline to the elliptical figure of the con- 
ducted The plate was screened from radiations of the 
flame which heated the wire, but was not shielded from 
currents of air, nor was unequal: radiation of the iodide specially 
prevented. The method of measurement was as follows: after 
the ellipse was well formed, and of permanent ew the 
extremities of its longer and of its shorter axes were mar 
scratching through the iodide with a very slender steel aC 
pen plate was then removed, and the lengths of the axes deter- 
ined by means of dividers and a scale divided into half 
millimetea 
