758 General Notes. [September, 
curves thus obtained, will not be visible to the naked eye, but if 
placed under a microscope and magnified twenty (20) diameters, 
their form can be plainly seen. his method of record has 
another advantage. Donders has remarked that a recording appa- 
ratus is only accurate for movements of a certain rapidity, for 
which it has been constructed, and if it is made to record. move- 
ments of much greater rapidity, they are not accurately rep- 
resented. But the microscopic inscription multiplies almost in- 
definitely the field of work for the graphic method, by obtaining 
a sufficiently fine steel point to write, and a black layer thin 
enough to receive the tracing. M. Marey has already succeeded 
in receiving and registering the movement of a tuning fork vibra- 
ting two hundred (200) times per second, and in recording the 
vibrations of a voice singing at one end of a tube. Even the 
vibrations of blood in a vessel, which causes the “bruit de 
souffle,” seem to be among the movements which can be recorded. 
At least, in the case of elastic tubes and artificial aneurisms, M. 
Marey has succeeded in recording the vibrations produced by 4 
current of water, and which are also audible. A possible source 
of error in this method, which must not be overlooked, is the 
friction of the style against the glass. Momentum and friction 
are two sources of possible error in all tracings. The former 
necessary to reduce the friction to a minimum to avoid this 
error.—/onudon Lancet, | 
are 
printed in life-like colors, while the text is so arranged that the 
exquisite sea weeds of our coast, hitherto determined with diffi- 
Abbe, of Jena, to whom we are indebted for the first and on 
rational solution of this complicated problem. Taken in connec- 
tion with recent papers by Professor Abbe himself, the modern 
doctrine of wide-angled objectives and resolving power 1S now 
for the first time fairly within reach of English readers. 
