Miscellanies. 399 
constructed on this principle, was stated to have a far greater directive 
energy than any instrument, of the nature of a compass, previously 
constructed. Since that period Mr. Scoresby has been pursuing, as 
opportunity offered, an extensive series of investigations on the sub- 
ject; both as to the law of combination in steel plates and bars, and 
as to the effect of temper, thickness, &c. on the aggregate power ; 
with the view of producing more powerful instruments for determin- 
ing the delicate variations in, and the actual condition of, the earth’s 
magnetism; a subject now engaging attention in some of the princi- 
pal observatories in Europe. The results, which have been success- 
ful beyond the objects originally contemplated, have been recently 
communicated to the Institute of France. One of these results likely 
to be of much importance in magnetical science, to which it is exten- 
sively applicable, is that of producing permanent artificial magnets of 
almost unlimited power. On the principle of construction of com- 
pound magnets hitherto adopted, only a very limited number of bars 
could be combined with advantage,-in consequence of the great de- 
of two feet in length and about th of an inch in thickness, that the 
first six plates received so much power that no additions, however 
great the number, were capable of producing more, in the aggregate, 
than about double that power. Aiming, however, to counteract the 
tendency to such rapid deterioration, Mr. Scoresby made some mag- 
netical combinations of perfectly hard steel plates, (which he has a 
ready method of magnetizing and testing,) by means of which an al- 
most unlimited power can be obtained. Already this combination has’ 
been carried, with no inconsiderable augmentation of the aggregate . 
energy, to the very last, to the extent of several dozens of hard plates, 
15 inches in length, so as to produce, by such combination, a com- 
pound magnet of very extraordinary power for its mass. The appli- 
cation of this principle to apparatus for magnetic electricity will ob- 
viously be of much advantage for compactness and power; whilst the 
application of the discovery to variation needles, dipping needles, and, 
probably, to sea compasses also, promises to be of much importance 
in experimental science, as well as for practical and economical pur- 
poses. Mr. Scoresby’s investigations have also led to other practical 
results, such as the means of testing most rigidly the quality and tem- 
per of steel plates, and of bars intended for compound magnets on the 
ordinary construction, by which the best plates can be selected and 
most powerful combinations may be obtained.—Lond. and Edin. 
sieioa Mag., April, 1838. 
