422 Scientific Intelligence. 
case be produced by the mechanical admixture of foreign coloring 
matter. Is it not possible that the difficulty of expressing the composi- 
tion of certain minerals by chemical formulas may arise from such aa 
admixture of coloring matter, the optical characters of these minerals 
having hitherto entirely misled us ?—w. G. 
. Rate of transmission of impressions made upon the nerves.— 
Hetmuoutz has communicated to the Physico-Agricultural Society of 
Konigsberg a paper on the methods of measuring very small portions 
of time, and on their application to physiological purposes. ‘The au- 
thor alludes in the first place to the remarkable difference observed by 
astronomers between the observations of different individuals and 
termed by them the personal equation. ‘The measurements of eac 
tus of Siemens for the measure of the velocity of a musket or cannon 
ball is next described in its general features. This apparatus only dif- 
takes place at the instant of this passage. In this manner the me du- 
ring which the ball traverses a space of half a line may be measured. 
The author next alludes to the principle of the revolving mirror due to 
Wheatstone, and used with so much success by Fizeau and Foucault. 
Finally he gives an account of the method of Pouillet as modified an 
used by himself. This consists in causing the galvanic current to act 
upon an oscillating magnet, observing this magnet by Gauss and We- 
ber’s method, and determining the constant factor necessary 10 convert 
differences of oscillation into differences of time. In this manner ac 
curate determinations could be made up to the zgdgath of a second of 
time. The physiological questions which the author sought to solve 
were these. In the transmission of intelligence, is a measurable ime 
necessary for the ends of the nerves 10 communicate to the brain the 
distant muscle? By operating with the muscle of a frog severed from 
the body of the animal but connected with the nerves proceeding from 
it, the author found that the activity of the muscle is by 90 means In- 
stantaneous, but appears sometime after the excitation of the — 
i afier- 
wards. The object was to show that the different stages of activity 0 
the muscle take place later when the excitation has to pass throug 
greater length of nerve, and this is actually the case. ‘The most prob 
able value of the velocity of propagation in the motor nerves of the 
frog was found to be 26-4 metres or about feet per second. 
results of the author’s experiments upon the human subject were ae 
follows: The intelligence of an impression made upon the ends ms 
nerves in communication with the skin is transmitted to the brain Wi 
