428 Mr. HE. H. Hall on the Rotation of the 
Soft Iron. 
The dimensions of the strip of soft iron used in the experi- 
ments were roughly as follows :— 
Length between terminals B, B (fig.1) . 2°9cm. 
Widths bo pee ieee skys. ete een 
dbniekmess, (c | wean ye eS OAS era 
Like the strip used in 1882* it was obtained through the 
kindness of Prof. Langley, of the Allegheny Observatory, and 
the two strips had probably nearly the same composition and 
character. 
Although the test made in 1882 was noé satisfactory, it 
seemed to me to indicate that the R. P. of soft iron was 
slightly greater at high than at low magnetic intensities, and 
I hazarded the opinion that future experiments would prove 
this to be the case. This opinion has scarcely been justified 
by the result. The table given below does indeed appear to 
indicate a very slight increase in the R. P. as M rises from 
801 to 3264, and again as M rises from 3264 to 5835, but 
the increase in the numbers, as observed, is too slight to deserve 
any confidence. 
| | | Estimated R.P. 
Date. Merny |e Wigs: ee | at 28°. 
Aug. 22,°88.| 62 | 791-4 [1771 | +7147x10-" 
. 282 | 797-6 | -1742 | +8302 
; 28:3 | 8046 |-1794 | +8304 
ee 
28:25 | 801-1 8303 +8290 x 10-15 
Aug. 23. 28°1 | 3259 | -1728 8306 
3 28°4 | 3274 | -1702 8289 
7. 27°65 | 3260 | 1696 8306 
—__.. 
28°05 | 3264 8300 +8297 x 10-15 
Aug. 24. 287 | 5797 |-1839 | 8391 
. 28:1 | 5833 |-1842 | 8310 
¢ 98:0 | 5875 |-1858 | 8245 
28:27 | 5885 8315 +8300 x 10-15 
Aug. 27. 97-25 | 8626 |-1894 |. 8139 | 
? 28:35 | 8690 |-1898 | 8261 
ip 27°95 | 8636 |-1911 | 8200 
27°85 | 8651 8200 4.8208 x 10-8 
Fall of R. P. for 1° fall of temperature equals approximately 3 per cent. 
* Silliman’s American Journal, March 1883; and Philosophical Maga- 
zine for May 1883. 
