A. D, Bache on the Horizontal Component of Magnetic Force. 261 



379. Poa andina, Nutt. in herb. Acad. Philad. " Upper Clear Creek " 



376. Poa arctica, R. Br. ? (P.Jlexuosa, Wahl.) ; a form of P. laxa? 

 ^Alpine ridges." 



377. Trisetum subsp{catum,Be3i\iY. " Alpine ridges." 



378. Bromus Kalmii, Gray, Man. " S. Clear Creek ; July." 



380. Fesluca ovina, L. " Alpine." 



381. Triticum eegilopoiJes, Turcz. Perhaps a variety of T. caninum, 

 as Ledebour has it. "Alpine." 



382. Phleum afpinum,L. "Subalpine." 



383. 387, 389. Carex atrafa, L., var. niffra, Boott. {C. nigra, All.), ex- 

 cept that the perigynia are light-colored. From the Var. ovata, Boott 

 (C. ovata, Rudge), they differ in the sessile and crowded spikes. 



384. CarextigidaX 



385. Carex incurva, Lightf., with a dense, globular head. 



386. Carex capillars, L. 

 388. Carex aurea, NutL 



390. Carex lanuginosa, Michx. S. Clear Creek. 

 891. Carex /estiva, Dewey. S. Clear Creek. 



393. Carex bromoides, Schk. ? Too young. 



394. Woodsia obtusa. Ton. "Subalpine." 



395. Cg/ttopteris fragilis, Bernh, 



396. Allosorus {Gymnogramme) acrostickoides ; referred by Sir Wm. 

 Hooker to A. crispus. " Alpine." 



397. JSfotocUoena dealbata, Kunze. Near Idaho. 



Art. XXIY.— Abstract of a discussion of the Horizontal Compo- 

 nent of the Magnetic Force, from observations made at the Girard 

 College Observatory, Philadelphia, in the years 1840-'41-'42- 

 '43-'44-'45 ; by A. D. Bache, LL.D., F.R.S., Mem. Corr. 

 Acad. Sc. Paris, Sup't, U. S. Coast Survey. 



r the full paper, notes of all the 



*-^ wie luii paper, notes oi all me cnau^ea m tuc iuouiui.^,vi..-o 

 trom accidental aerangeraent or otherwise, and of the corrections 

 applied, follow this statement, as an introduction to Table No. I, 



which contains the recapitulation of the monthly mean readings 

 of the bifilar magnetometer, corrected so as to present a continu- 

 ous series and with the observed temperatures. . , . 



in applying the results, by equations of the form involving 

 tne change of temperature and of epoch, the latter cbang^ in- 

 eluding the loss of magnetism in the bar and the change of the 

 J|orizontal force of magnetism, it was found expedient to omit 

 the results of the first year of the series. The remaming four 

 years results gave 16-5 scale divisions for the monthly effect of 

 ^^e change of magnetic horizontal intensity, and of the magnet- 



