14 H. A, Rowland—Magnet’c Proof Plane. 
changes of wind and temperature. I do not think that these 
sudden changes can be fully explained by the supposition of a 
polar current sweeping along the earth’s surface from a higher 
to a lower latitude, but it seems necessary to admit a sudden 
transfer of very cold air from a higher to a lower level. 
The heat of Jan. 14th probably resulted from the sudden pre- 
cipitation of vapor caused by the elevation of air from the 
earth’s surface; and this warm air near the earth’s surface sud- 
denly ascended on the 15th, being displaced by the colder air 
of a greater elevation. : 
n ied the materials for this article, I have been 
assisted by Mr. Edward S. Cowles, a graduate of Yale College 
of the class of 1878. 
Art. 1].—Preliminary Note on a Magnetic Proof Plaue; by 
Henry A. ROWLAND. 
AxsouT four years ago I made a large number of experi- 
ments on the distribution of magnetism on iron and steel bars 
by means of a coil of wire sliding along the bar; the induced 
current in the coil as measured by a galvanometer was a meas- 
ure of the number of lines of force cut by the coil and can be 
found in absolute measure by my method of using the earth 
inductor. These researches have never yet been published 
owing to cireumstances beyond my control, but are known to 
quite a number of persons in this country, and will soon be 
published. The method there used is the only correct one that 
I know of for experimenting on magnetic distribution, and my 
purpose in this note is to extend it to bodies of all shapes, so 
that experiments on magnetic distribution may become as sim- 
ple and easy to perform as those on electrical distribution. And 
so well has my magnetic proof plane accomplished this that I 
can illustrate the subject to my classes with the greatest ease. 
The 5 eapoee required is merely a small coil of wire $ to 4 
inch in diameter, containing from 10 to 50 turns, and a Thomson 
galvanometer. When we require to reduce to absolute measure, 
another coil about a foot in diameter and containing 20 or 30 
turns is required. Having attached the small coil (or, as I call 
it, the magnetic proof plane) to the galvanometer, we have 
merely to lay it on the required spot, and when everything is 
ready, to pull it away suddenly and carry it to a distance, and 
the momentary deflection of the galvanometer needle will be 
proportional to that component of the lines of force at that 
point which is cccioteate: to the plane of the coil. And if 
we apply it to the surface of a permanent magnet the so-called 
