200 
Prof. J. Henry’s Contributions 
female. All the following sizes common : l-4-3G5th, J -4268th, 
1-41 73rd, and l-4000th. Extreme sizes 1- 5333rd and 
l-3555th of an inch. Blood from a prick of the nose. 
135. Alexandrian Rat, [Mus Atexandrinus, albino, var.,) 
an adult male. l-4173rd, l-4000th, l-3810th, and l-3764th, 
very common sizes. Small corpuscles l-4800th; the large 
l-3200th. Edges of disks 1~ 14,000th of an inch thick. Blood 
from a vein of the hind leg. 
136. Coendu or Ring-tailed Porcupine, (Synetheres pre- 
hensilis,) a full-grown male. Common diameters 1 -3428th, 
1 -3309th, and l-3600th. Extreme sizes l-4570th and 
1 -2460th of an inch. Blood from a cut at the end of the 
tail. 
Error in the last paper (No. 2.) p. 108, 1. 28, for Haller, 
read Harvey. 
XXXVII. Contributions to 'Electricity and Magnetism. 
No. III. on Electro-magnetic Induction. By Joseph 
Henry, LL.D.^ Prof, of Natural Philosophy m the College 
of New Jersey, Princeton^. 
Introduction. — Section I. Conditions which infuence the 
induction of a Current on itself . — Section II. Conditions 
which infuence the pro deletion of Secondary Currents . — Sec- 
tion III. On the Induction of Secondary Ciirrents at a 
distance . — Section IV. On the Effects produced by in- 
terposing different Substances between the Conductors . — Sec- 
tion V. On the Production and Properties of induced 
Currents of the Third, Fourth and Fifth Order . — Section 
VI. The Productio7i of induced Currents of the different 
Orders from ordmary Electricity . — Note on the investiga- 
tions ofProfessor Ettingshausen. 
1. QINCE my investigations in reference to the influence 
^ of a spiral conductor, in increasing the intensity of a 
galvanic current, were submitted to the Society, the valuable 
paper of Dr. Faraday, on the same subject, has been published, 
and also various modifications of the principle have been made 
by Sturgeon, Masson, Page, and others, to increase the ef- 
fects. The spiral conductor has likewise been applied by 
Cav. Antinori to produce a spark by the action of a thermo- 
electrical pile : and Mr. Watkins has succeeded in exhibiting 
all the phsenomena of hydro-electricity by the same means. 
Although the principle has been much extended by the re- 
* From the Transactions of the American Philosophical Society, vol. vi, 
having been read Nov. 2, 1838. 
