Miscellanies. 205 



power, I would suggest what may be called a compound electro-mag- 

 net. I propose to have a series of circles, encircling each other to 

 any definite extent required. I would after having formed a primary 

 electro-magnet have it insulated on the outer surface ; then place 

 either a cylinder of iron or a succession of wires, until they have 

 encircled the primary electro-magnet ; then make a helix of copper 

 wire in the usual manner ; (I would prefer platinum wire to make the 

 helix; ) after having made a number sufficient to try an experiment, 

 unite them by a plate of iron, either entire or in rims corresponding 

 to each magnet. I also suggest the trial of brass cylinders over each 

 successive electro-magnet to cut off the radiations of electricity; this 

 will have either the effect to increase or decrease the magnetic power ; 

 experiments thereon must determine. Not having leisure to pursue the 

 subject myself, I offer these suggestions for the public good through 

 the medium of your highly valuable Journal. 

 Yours respectfully, 



Jonas Humbert, Jr., Medical Electrician, 



327 Broome St., New York City. 



7. Exchanges of American Shells and Insects. 



To THE Editors — Gent. : — I have for several years spent much 

 of my leisure time in collecting the fresh-water and land shells of this 

 state, and have on hand a large number of species of Unio, Marga- 

 ritana, (Alasmodonta,) Anodonta, Cyclas, Ancylas, Helix, Polygyra, 

 Helecina, Pupa, Succinea, Cyclostoma, Planorbis, Physa, Lymneus, 

 Melania, Anculosa, Valvata, and Paludina, which I am desirous of 

 exchanging for such native and foreign species as are not in my col- 

 lection. My shells are generally very perfect ; the Naiades, which 

 are mostly from the Scioto River and its tributaries, are remarkably 

 so. I am particularly desirous of exchanging for native shells in the 

 above genera, especially for native and foreign Naiades. 



I am also collecting the Insects of this state, and would be pleased 

 to exchange them for native and foreign labelled species. 



I can label my shells with the names by which they are known to 

 our western naturalists. 



Either this fall or early in the spring I will do myself the pleasure 



of sending for your acceptance a suit of western shells. 



I am respectfully, your obedient servant, 



C. S. Ward. 

 Roscoe, Ohio, November ]4, 1839. 



8. The Railway Magazine and Steam Navigation Journal. Ed- 

 ited by John Hera-path Esq. London. PubHshed by J. Wyld. 8vo. 

 Monthly. — This is a periodical work devoted chiefly to what is now 



