20 Notice of a Shooting-Star. 
ray. By means of an endless screw, by which the prisms 
may be rotated equally on their axis, through an angle of 
90°, the polarizing spectacles may be used as a picture po- 
lariscope. By the aid of this instrument, a picture hung in 
a bad light, or too highly varnished, appears fla¢, and can be 
perfectly seen. 
3. Polarizing Diaphragm for the Microscope. 
This instrument is attached to the microscope in the same 
manner as Messrs Smith and Beck, of London, adapt their 
polarizer to the stage. It consists of two Nicol’s prisms, one 
of which is fixed, the other being allowed rotation through 
an angle of 90°, on the same axis as the fixed prism. By 
this arrangement, the light can be modified from its greatest 
brillianey to total darkness. 
4, Surgical Polariscope. 
This instrument is intended to aid the oculist when ex- 
amining the cornea of the eye ; it is a Nicol’s prism placed in 
a tube behind a lens of long focus, which rotates freely on 
its own axis, to suit the varying plane of the polarized ray 
from the cornea. It thus enables an oculist to observe any 
minute foreign body on the cornea with ease, as the glare 
from the surface is entirely removed. 
Notice of a Shooting-Star ; and on a Method of Cooling the 
Atmosphere of Roomsin a Tropical Climate. By Professor 
C. P1azzi SMytH, F.R.S.E., &e. 
1. Notice of a Shooting-Star. 
The object of this notice was merely to call attention to 
the importance of observing the phenomena of shooting-stars 
more carefully and rigidly, and of applying to them, more 
correctly than has generally been the case hitherto, the 
measurement of time and of space, and to exemplify what 
may be done in this way by the calculation of a recent in- 
