Contributions to Electricity/ and Magnetism. 117 



eric name. It will be placed in a natural order immediately after 

 Pholcus. 



Subgenus Spermophora. 



Eyes, six, in two clusters, one on .« §» 

 each side of the cephalothorax, thus -^ ^ 



Legs, the first pair longest, then the fourth and seco7id, nearly 

 equal, the tlw^d pair shortest. Length moderate, slender. 



Lip, wide, triangular. 



Maxillce, tapering towards the point, inclined over the lip. 



MandihulcB, short, conical, with very small fangs. 



The characters derived from the trophi, are nearly those of 

 Pholcus, but the absence of the two eyes in front of the cephalo- 

 thorax, would alone, remove this spider from that subdivision. 

 Moreover, the legs, which in Pholcus are excessively long, are here 

 of a moderate length. This spider, which is wholly of a pale hue, 

 makes its very loose web in dark places, under rubbish. The 

 female carries in its mandibles its eggs glued together without 

 any silk, until they are hatciied. Inhabits Alabama. 



This species, the 137th of my MS. catalogue, is there named 

 Spermophora meridionalis. Of the 147 species comprised in this 

 catalogue, there are not ten mentioned in European works, besides 

 those described by Bosc, whose manuscript was never printed.* 



Florence, Ala., September 2, 1839. 



Art. XIII. — Contributions to Electricity and Magnetism. — 

 No. IV. On Electro-Dynamic Induction; by Joseph Henry, 

 LL. D., Professor of Natural Philosophy in the College of New 

 Jersey, Princeton. Read June 19, L840.t 



(Continued from p. 243, Vol. xx.kviii, No. 2, of this Journal.) 

 INTRODUCTION. 



1. In tlie course of my last paper, it was stated that the inves- 

 tigations which it detailed were not as complete in some parts as 

 I could wish, and that I hoped to develop them more fully in 



* A valuable catalogue and description by Prof Hentz, of the genera of Ara- 

 neides found in this country, was published in this Journal, Vol. xxi, p. 100 — 109, 

 1832.— £rf^. 



t From the Transactions of the American Philosophical Society, Vol. 8, N. S. 



