4 
Optics.—Microscopes for Micrographic demonstration. 105 
This idea of deriving the heat from motion, which was rejected more 
than thirty years ago, suggests the hypothesis which assigns an analogous 
origin to terrestrial and hence to planetary magnetism, an hypothesis of 
which we have spoken on several occasions in this Journal.* But, at 
that time, the question of solar magnetism was still under discussion, 
which, researches undertaken by M. Secchi, director of the Observatory 
at Rome, have now established on evidence. The sun, which is a 
source of heat, and a source of light, is then a source also of magnetism ; 
attained ; there are always numerous streaks in the mass, which cause 
- Peyronny, captain in the corps of Engineers at Cherbourg, pro- 
poses to avoid these difficulties, by giving the crucible a rapid rotatory 
movement around a vertical axis ; the centrifugal force tends to bring all 
the bubbles of air about the centre of the melted mass, whilst the streaks 
caused by the stirring mostly disappear, and those remaining are circu- 
lar and feeble, and also little objectionable if the axis of the mass be 
made the axis of the lens. 
t we have not, properly speaking, an ratus for measuring easily 
and rigorously the quantity of polarized light contained in a ray or in 
ven luminous field. rnard, Pro ro sics at Bor- 
and also profiting by the discoveries of Babinet and Beer of Bonn, M. Ber- 
n constructed an instrument of extreme delicacy, which is man- 
aged with great ease, and requires but two minutes for an observation. 
directed with a needle. The microscopes of Nachet realize this object, 
have been employed by Prof. Milne Edwards for a year in his lec. 
-- _-*® January 1854, p. 116, and November, 1854, p. 386. 
Stconp Szares, Vol. XIX, No. 55—Jan,, 1855. 14 
