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expanded air. 
January I, 1914] 
NATURE 
in advanced algebra. The subject is abstract, and 
deals with topics and ideas relatively unimportant for 
the student. Yet advanced algebra is often taught 
as a pre-requisite to calculus. It is unfortunate to 
force the freshman through an extended course in 
analytic geometry.’’ This latter reference makes one 
wonder what Prof. Wilson would think of our recent 
epidemic of ‘‘ projective geometries,” good, bad, and 
indifferent, which may teach pupils to copy out proofs 
of stereotyped bookwork like Pascal’s or Brianchon’s 
theorems, but will never enable them to attempt a 
problem in mechanics involving a conic, cycloid, or 
catenary except by writing down the equation of the 
curve and becoming involved in hopelessly intractable 
formulz from which the answer ‘‘may be obtained ”’ 
—perhaps by the examiner, but with little credit and 
no educational value to the candidate. 
IN connection with the recent International Con- 
gress of Refrigeration held at Chicago and Washing- 
ton, the Smithsonian Institution has directed atten- 
tion to the first U.S. patent for the manufacture of 
ice, granted on May 6, 1851, to John Gorrie, of New 
Orleans, and now on exhibition in the U.S, National 
Museum. The patent fully describes the method of 
compressing air toa small part of its bulk, abstracting 
the heat liberated by a jet of water, allowing the air 
to re-expand in an engine, whereby the expansion is 
utilised and helps in the working of the condensing 
pump, injecting an uncongealable liquid into the engine, 
and circulating it as a medium to absorb heat from 
the water being frozen, and to give it out to the 
“The employment of the engine for 
the purpose of rendering the expansion of the con- 
densed air gradual, in order to obtain its full re- 
frigeratory effects, and, at the same time, render 
available the mechanical force with which it tends to 
dilate to aid in working the condensing pump, irre- 
spective of the manner in which the several parts 
are made, arranged, and operated” is a remarkably 
accurate description of the method for the time. Short 
of the actual recognition of the equivalence of work 
and heat, due to Mayer in 1844, the inventor’s ideas 
could scarcely have been clearer. Gorrie published 
in 1844 several articles on the subject in The Com- 
mercial Advertiser of Apalachicola, Fla., a_ re- 
examination of which might be of interest from the 
point of «view of the history of the dynamical theory 
of heat and the law of the conservation of energy. These 
papers, together with the original of the patent, have 
been deposited in the U.S. National Museum. 
Part vi. of vol. xxi. of the Memoirs of the Indian 
Meteorological Department contains a discussion by 
Dr. G. C. Simpson of the potential gradient of atmo- 
spheric electricity at Simla. The data were derived 
from a Benndorf electrograph between May, 1907, 
and May, 1910, with an interruption between October 
and November, 1908, when the site of the instrument 
was altered. There are two tables showing respec- 
tively the annual variation of the potential gradient, 
and its diurnal variation for the twelve months of the 
year, for four quarters and for the year as a whole. 
Two plates show the results graphically. Use is made 
only of the days free from large irregular disturb- 
NO. 2305, VOL. 92] 
511 
ances, numbering altogether 440. Owing to the non- 
existence of any sufficiently extensive level ground in 
Simla, it was impossible to deduce absolute values 
appropriate to a site in the open. The unit employed 
is thus an arbitrary one. The most remarkable 
feature is the frequent occurrence of negative potential 
in fine weather during May and June. This Dr. 
Simpson attributes to the presence of large quantities 
of dust in the atmosphere during the warm, dry 
weather which precedes the setting in of the monsoon. 
The number of days available, especially in July and 
August, is scarcely sufficient to give smooth diurnal 
inequalities for the individual months of the year; 
but there are obviously as a rule two maxima and 
two minima, one pair in the forenoon, the other in 
the afternoon. The morning minimum is usually the 
principal one, especially towards mid-winter, but in 
April, May, and June—especially June—the minimum 
in the early afternoon is the more prominent. On 
the average of the years included, February gave the 
highest and June the lowest mean value of the poten- 
tial. 
A new method of preparing aqueous colloidal solu- 
tions of metals is described by H. Morris-Airey and 
J. H. Long in the Proceedings of the University of 
Durham Scientific Society (vol. v., part ii., pp. 68 and 
113), Which is based on the use of high-frequency 
alternating currents passing between electrodes of the 
metal immersed in water. It is possible to vary the 
range of frequency of the current between very wide 
limits, and in this way it has been shown that the 
colour supposed to be characteristic of the colloidal 
solutions of metals is a result of the special conditions 
of the discharge. Thus gold, tor instance, on altering 
the frequency, can be made to give a red, blue, or 
purple solution; in the red solution the particles are 
negatively charged, and in the blue solution positively 
charged. The purple solutions contain both kinds of 
particles. The red solution is converted into the blue 
by the action of an electrolyte or electric field. 
WE learn from Engineering for December 26 that 
Prof. G. Benoit and Mr. Woernle are engaged on an 
investigation of the strength and durability of wire 
ropes. The research, which they are conducting in 
the laboratory for hoisting-machinery of the Technical 
High School at Karlsruhe, will occupy them for some 
time, but as the experiments are fairly conclusive 
regarding the deleterious influences of twisting, the 
preliminary results have been published. Twisted 
ropes have been proved by these experiments to be 
much less safe than the untwisted wires, even if the 
wires be annealed, thus demonstrating that the twist- 
ing leaves considerable strains in wire ropes, and 
especially on those made of high-class steels, which 
are chiefly used in mine haulage and winding. The 
method of experimenting consisted in applying the 
wires and ropes to a pulley which was turned to and 
fro through an angle of about go° at the rate of 
tooo turns per hour, thus bending and unbending the 
wires always in the same direction. Further experi- 
ments with alternating bending to different radii, &c., 
are now being made. 
