Auaeust 20, 1897. ] 
The multiple or oscillatory character of 
the electric discharge from a Leyden jar 
was discovered by Henry in 1842. It was 
carefully studied afterward by Feddersen, 
who used a revolving mirror, and yet more 
fully by Rood, who employed several 
methods, but more particularly that of the 
revolving disk with radial slits. Professor 
Mayer, in 1874, took advantage of centrifu- 
gal action to give steadiness to a disk of 
blackened paper rotated rapidly between 
the electrodes employed for transmission 
of the spark. The perforations were then 
subjected at leisure to micrometric measure- 
ment. Since the rotation of the disk is 
known, the means is thus afforded for 
measuring the duration of the discharge 
and the intervals between the successive 
sparks which compose it. The conditions 
were then studied for securing the most 
nearly simple discharge possible. This 
served as the necessary antecedent to the 
successful employment of the induction coil 
in conjunction with a method previously 
devised for measuring minute intervals of 
time with the tuning fork, or rating a 
tuning fork by comparison with a standard 
clock. The combination formed an admi- 
rable chronoscope for a variety of purposes, 
but more especially for measuring the 
velocity of projectiles. 
On the general subject of heat Professor 
Mayer published several articles. The first 
of these, in relation to waterfalls, has been 
already mentioned. In 1872 he devised a 
method of tracing the progress and deter- 
mining the boundary of a wave of conducted 
heat by taking advantage of the variation 
in color with change of temperature which 
is characteristic of certain double iodides. 
The same method was applied three years 
afterward to the securing of thermographs 
of the isothermal lines of the solar disk. In 
1890 he gave publication to a paper on the 
determination of the coefficient of cubic ex- 
pansion of a solid from the observation of 
SCIENCE. 
267 
the temperature at which water in a vessel 
made of this solid has the same apparent 
volume as it has at 0° C., and on the coef- 
ficient of cubic expansion of a substance 
determined by means of a hydrometer made 
of it. The method was applied to several 
different substances, including brass and 
vulcanite. This led to a general investiga- 
tion of the properties of vulcanite, which 
was published soon afterward. One of 
these properties is its remarkably large co- 
efficient of expansion, exceeding that of 
mercury. 
Soon after the publication of Rontgen’s 
discovery of a new species of radiation 
Professor Mayer’s interest in this was 
aroused, and in June, 1896, he published the 
outcome of his investigation of herapathite, 
which had been employed by him to test 
the possibility of polarizing the Rontgen 
rays. Formule were deduced for the trans- 
missive powers of several substances for 
these rays, including tourmaline, hera- 
pathite, glass, aluminum and platinum. 
Professor Mayer’s last scientific work was 
an experimental investigation of the equilib- 
rium of the forces acting in the flotation of 
dises and rings of metal, and an application 
of such rings to the determination of the 
measure of surface tension of liquids. The 
method was wholly new, and the agreement 
among results was remarkable. At best, it 
has been difficult in the past to secure relia- 
ble results in work of this kind, and the 
present work is fully equal, if not superior, 
to the best hitherto accomplished by Pla- 
teau and Quincke. It was done during the 
intervals between periods of acute physical 
suffering, and its appearance in the American 
Journal of Science for April of the present 
year preceded by only a few days the para- 
lytic stroke which demonstrated that the 
investigator’s life work was already ended. 
In this brief sketch of Professor Mayer’s 
labors but little has been said of his numer- 
ous happy devices for lecture demonstra- 
