200 Prof. J. Henry's Contributions 



female. All the following sizes common : 1 -43G5tli, J -4268th, 

 l-4-l73rd, and l-4000tb. Extreme sizes 1- 5333rd and 

 .l-3555th of an inch. Blood from a prick of the nose. 



135. Alexandrian Rat, {Miis Alexandrinus, albino, var.,) 

 an adult male. l-4.173rd, l"4000th, l-3810th, and l-3764th, 

 very common sizes. Small corpuscles 1 -4800th; the large 

 3-S200th. Edges of disks 1-1 4,000th of an inch thick. Blood 

 from a vein of the hind leg. 



136. Coendu or Ring-tailed Porcupine, {Synethercs pre- 

 7ie?isilis,) 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. 



XX XVII. Contributions to Electricity mid Magnetisiu. 

 No. III. on Electro-magnetic Induction. By Joseph 

 Henry, LL.D., Prof, of Natural Philoso^yJiy in the College 

 of New Jersey, Princeton* . 



Introduction. — Section I. Conditions which influence the 

 induction of a Current on itself. — Section II. Conditions 

 ivhich infliicnce the prodjictio7i of Secondary Currents. — Sec- 

 tion III. On the Induction of Secondary Currents 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 Production of induced Currents of the different 

 Orders from ordinary Electricity. — Note on the investiga- 

 tions of Professor Ettingshausen. 



1. CINCE 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 h^'dro-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. 



