Chemistry and Physics. 423 
a velocity which does not vary in different individuals, nor at different 
limes, of about metres, or 195 feet per second. Arrived at the 
brain an interval of about ;4th of a second passes before the will, even 
when the atiention is sirung to the uttermost, is able to give the com- 
mand to the nerves that certain muscles shall execute a certain motion. 
This interval varies in different persons, and depends chiefly upon the 
degree of attention. It varies also at different times in the case of the 
same person. When the attention is lax, it is very irregular, but when 
In all therefore from the excitation of the sensitive nerves till the mov- 
ing of the muscle 14 to two-tenths of a second are consumed. [For 
more ample details and for much matter of a highly suggestive char- 
acter, we must refer to the original lecture.]—L. §& E. Phil. Mag., 
Nov., 1853. 
3. Preparation of large crystals of sulphate of todo-quinine for 
optical purposes.—Herapatu has succeeded in obtaining crystals of 
this.very interesting and valuable substance of sufficient size to be sub- 
stituted for tourmaline in polarizing light. For the details of the pro- 
cess however, we must refer to the original paper—L. & E. Phil. 
Mag., Nov., 1853. 
4. On the law of induction in magnetic and paramagnetic subsian- 
ces.—PiucKer has communicated an elaborate memoir on this subject 
from which we shall content ourselves with abstracting the summary of 
results. These are as follows: 
(1.) In all magnetic and diamagnetic substances the same general 
law gives the intensity of the induced magnetism as a function of the 
exciting force. For each substance this law is particularized by the 
values of two constants. Of these two constants the one gives, as the 
inducing force vanishes, the ratio of this force to the induced magnet- 
ism (constant of induction), and the second determines the resistance 
which prevents the induced magnetism from increasing proportional to 
the inductive force (constant of resistance 
(2.) For every substance there is a po 
Constantly approximates as the inducing force increases. 
Diamagnetic substances (Bismuth, Phosphorus,) so far as the 
law of the imensity of their excitation is concerned, behave precisely 
like magnetic substances, though they exert a directly opposite action 
Upon the inducing magnetic pole. This similar behavior compels us, 
in my view, to assnme that the condition of a diamagnetically excited 
body is in itself in no wise different from the condition of a magneti- 
cally excited body, that furthermore polarity is also present in the exci- 
tation of diamagnetic substances, but that this is called forth by an in- 
duction which is the opposite to that which occurs in magnetic bodies. 
‘The curves which represent the law of induction for diamag- 
Netic substances are surrounded on both sides by the curves for mag- 
Netic substances. They show that the resistance which is opposed to 
the excitation of diamagnetic bodies is less than in most magnetic sub- 
stances, but by no means vanishes; on the contrary it is greater than 
in oxygen and hydrate of oxyd of cobalt. 
— 
int of saturation to which it 
