A. M. Mayer—Boundary of a Wave of Conducted Heat. 87 
works simultaneously in preparation for the coming era; and 
it is a gain to us in our contemplations, that we hence may bal- 
ance the beauty and repose of the tropics, through all the pro- 
gressing changes, against the prolehged scenes of glacial deso- 
lation that prevailed over large portions of the continents. 
Art. IX.—On a precise Method of tracing the Progress and of 
determining the Boundary of a Wave of Conducted Heat; b 
LFRED M. Mayer, Ph.D., Professor of Physics in the 
Stevens Institute of Technology, Hoboken, N. J. 
_ In 1870 Meusel experimented on the formation of double 
todides, and on the remarkable changes of color produced in 
these bodies by heat.* He prepared a double iodide of copper 
that experimented on by me) turns to a deep chocolate brown 
on heating to about 70° ©. In order forcibly to exhibit this 
change of color, Boettger moistened the iodide with weak gum 
Water, and painted it on paper; on heating the latter, the 
change of color is produced, and on cooling, the iodide regains 
its former brilliancy. 
Dr. G. F. Barker had the kindness to present me with a card 
So prepared, and on experimenting with it I soon perceived the 
valuable means it afforded of tracing the progress and of deter- 
mining the boundary of a wave of sontacred heat. To Dr. 
ker I am also indebted for the iodide used in the experi- 
ments I here present. 
The first use I made of this substance was to track the heat 
conducted by bars and plates of metal,+ and the sharpness of 
the boundary of the colors instigated me to test the value of 
18 mode of experiment, by applying it to a determination of 
the elliptical contour of the isothermal of conduction, in the 
Principal section of a quartz crystal. : Stee 
harmont, in his beautiful researches on this subject (Ann. 
de Ch. et de Ph., 3¢ S., t. xxi, xxii), has carefully determined 
the ratio of the axes of this elliptical figure, by coating a thin 
Sngitudinal section of the crystal with wax, and leading 
through it a silver wire, by means of which heat was brought 
- Ber. Berl. Chem. Ges, iii, 123, 1870. Bul. Soc. Oh., H, xiii, 220, 1870. J. Pr. 
Ti. ii, 136, Aug, 1870. 
He iodide is decomposed by contact with certain metals; these should be 
‘balan With a film of collodion, or electrotyped with copper before applying the. 
