86 REPORT—1849. 
counting from the zero mark, 0, on each series; and it is affixed to T by a 
milled screw passing through one of the oblong slits at either end, so that 
either scale may be used, or a blade much more minutely divided might be 
substituted. 
A good double lens, or pair of lenses, may be used upon a stand with this 
apparatus for reading the scales. 
The manner of using this instrument is perhaps sufficiently obvious. The 
zero of the ordinate scale (t') is adjusted (if necessary) to that right-hand 
edge and extremity of the zero line (y*) which is furthest from the me 
scale, M, transversely (after relaxing the screw near T). The ordinate 
scale is, secondly, applied to the other extremity of y*; and if the zero point 
on it should not coincide with y®, then the screw c! is relaxed, and the ap- 
propriate left-hand screw (either c® or c°) is slowly screwed up until exact 
coincidence occurs. Then ce! is screwed up again. 
Particular information, &c. as to the use of the apparatus sent to Toronto 
was carefully detailed, and some hints relative to the (seemingly) best modes 
of operating upon the Jong Daguerreotype plates, &c. were set down for the 
use of Captain Lefroy, &c. 
These details are not requisite here. The former kind of information has 
been already published, ¢.e. when my earlier experiments on registration 
were made known* ; and the latter is comprised in great part (although not 
in sufficient abundance) in several well-known publications. 
Proceeding now with the relation of the other circumstances connected 
with experimental inquiry at Kew, I may add, that at the visit above men- 
tioned of Colonel Sabine we held some conversation on the subject of con- 
structing a vertical-force magnetograph, which had previously occupied our 
attention, when the Colonel relieved me from a difficulty by hinting that an 
arm might be erected vertically upon the centre of the magnet, to carry the 
shield with its slit. By this means the injurious proximity of the Jamp to 
the magnet at night will be entirely avoided. 
This apparatus is in an advanced state of preparation for Toronto. 
My correspondence with the Rev. Alfred Weld, respecting the establish- 
ment of a self-registering electric and magnetic observatory at Stonyhurst, 
after occupying much time (in making plans, drawings, &c.), has not been 
as yet followed by the erection of a suitable building at that locality. 
In August 1848 I received from the Superintendent of the Great Western 
Railway Electric Telegraph some further and rather curious notices of the 
deflections of the needles, &c. at Paddington, Slough and Derby. At Pad- 
dington, on the 9th of August, at about 1" 50™ p.n:., during a storm, an ex- 
plosion occurred in the office like that of a gun fired, and the cross wire was 
fused. The same thing occurred at Slough at the same time. 
. The most remarkable effects upon these wires are those which are pro- 
duced by fogs; and I apprehend that experiments relative to them would be 
interesting, and perhaps profitable. 
Amongst several distinguished visitors to the observatory in the past year, 
Don Manuel Rico, Director of the Madrid Observatory, came to converse 
on the subject of erecting an electrical apparatus like ours at that building, 
and gave me a rough plan and description of it. 
The site appears to be extremely favourable. Experiments and observa- 
tions in that latitude would form an important link in a geographical series 
comprising the observations (now probably going on by means of similar 
apparatus) at Bombay, and others to be instituted in a very high latitude (as — 
Alten, e.9.). 
* Vide Phil. Trans., Part 1. for 1847. 

