G 32 
PROFESSOR J. A. EWING ON EXPERIMENTAL 
was applied, which neutralised the greater part of the earth’s field at the magneto¬ 
meter needle, leaving only a small directive force, whose intensity was estimated 
by comparing the period of the needle with its period when this directing magnet 
was removed. Further, the magnetism of the wire or non pipe under examination 
was sufficiently balanced by a second deflecting magnet (arranged to deflect the 
magnetometer without altering its sensibility) to bring the spot of light on the 
scale. To determine what ratio the observed magnetic changes bore to the whole 
magnetism, it was only necessary to observe the whole deflection due to the mag¬ 
netised wire or pipe, with the magnetometer in an insensitive state, and measure 
(by comparing periods) the relative sensibility of the two states of the magnetometer. 
Much time was spent in tentative experiments before satisfactory results were 
obtained. These, however, when they were arrived at showed so conclusively that 
within the limits of temperature experimented on there was no sensible hysteresis in 
the relation of magnetic change to temperature, that the subject was not pursued at 
any great length ; and for the same reason it will suffice to quote a single set of 
observations. 
§ 116. (November 30, 1882.) In this experiment the magnetising field was the 
earth’s vertical force, in which the iron under test was shaken beforehand. Then 
water and steam were passed alternately, five times each, after which the following- 
readings were taken. The numbers given are the actual magnetometer readings : by 
adding 17,000 to them they can be made approximately proportional to the total 
magnetisation of the piece. The arrows show the sequence of the changes. 
Water. Ether vapour. Alcohol vapour. Steam. 
(14° C.) (35° C.) (78|° C.) (100° C.) 
413 
380 
415 
383 
381 
415 
381 
383 
/ 
382 
416 
/ 
382 
418 
382 
\ 
CO 
CO 
CO 
302 
\ 
304 
X 
301 
\ 
304 
/ 
305 
\ 
303 
/ 
304 
\ 
304 
305 
263 
261 
262 
262 
It is clear from these figures that the changes of magnetism 
o o o 
between 14° C. and 
