Natural Philosophy.’ —Magnetism. I8S 
line, the divisions being read off with a small eye-glass at the 
other end of the tube. When distinct vision is obtained in the 
telescope, the small tube is held against the eye-glass of the 
telescope, and the observer sees how many divisions of the scale 
are occupied by the small luminous circle in the centre of the 
eye-glass. The clear diameter of the object-glass is then di- 
vided by this quantity, and the quotient is the magnifying 
power. This apparatus was first described in the Ephemerides 
de Berlin for 1775. Mr Ramsden had, fifteen years before, 
constructed a similar instrument, i» which he measured the 
diameter of the small luminous circle, by the extent of the two 
images formed by two semilenses. — See the Bibh IJniverselle , 
Sept. 1822, p. 6. Note. 
MAGNETISM. 
4. Magnetism of the Violet Rays. — The Royal Academy 
of Sciences of Lyons, have offered a prize of 300 francs, for a 
solution of the interesting question respecting Morichini’s ex- 
periments on the magnetising influence of the violet rays. (See 
this Journal , vpl. i. p. 239.) The competitors are required a to 
shew, by decisive experiments, if the violet ray of the solar spec- 
trum possesses the virtue of communicating magnetism to the 
unmagnetised needle of steel ; — if this virtue belongs to it, 
to the exclusion of the other coloured rays - and, in short, 
if this species of communicated magnetism, attributed to the 
violet light, is real or illusory.’ 1 In the programme of this 
prize, it is stated, that Professor Configliachi of Pavia, found 
that the same kind of magnetism was communicated by every 
other ray of the simple light of day, and even in total dark- 
ness. The memoirs to be sent to MM. Mollet and Dumas, Se- 
cretaries, before the 30th of J une 1 823. 
5. Steinhauser's Method of making Artificial Magnets . — - 
Professor Steinhauser has found, that the usual operation of 
double touch should be performed in a circle ; and that, in mag- 
netising horse-shoe magnets, two of them should be placed with 
their friendly poles together, and the touch performed circu- 
larly. Upon the separation of the two horse-shoe magnets, a 
considerable part of their force is lost, unless the great circuit is 
previously formed into two smaller ones, by joining the poles of 
