1877 **] Scientific Notes. 429 
5. Otheoscope.— A large horizontal coloured disk, of roasted mica, driven by 
inclined aluminium vanes placed underneath it. 
6. Otheoscope. — A bright aluminium disk cut in segments, and each 
segment turned at an angle, driven by a similar one below of lampblacked 
silver. 
7. Radiometer. — A vertical radiometer, made with eight disks of mica 
blacked on one side, and the whole suspended on a horizontal axis which 
works in two glass cups. The motion of the radiometer is assisted on each 
side by driving vanes of aluminium blacked on one side. 
8. Radiometer. — A vertical turbine radiometer, the oval vanes of roasted 
mica blacked on cne side. 
9. Radiometer. — A spiral radiometer of roasted mica blacked on the upper 
side. 
10. Radiometer of large size, showing great sensitiveness. 
ir. Radiometer. — A two-disk radiometer, the fly carrying roasted mica disks 
blacked on one side; in front of each black surface is fixed a large disk of 
thin clear mica. The molecular disturbance set up on the black surface, 
and streaming from it, is reflected in the opposite direction by the clear plate 
of mica, causing the fly to move abnormally, i.e., the black surface towards 
the light. 
12. Radiometer. — A two-disk radiometer, the fly carrying roasted rmca 
disks blacked on one side, similar to No. n, but with a large clear disk on 
each side. The molecular disturbance, prevented from being reflected back- 
wards by the second clear disk, is thus caused to expend itself in a vertical 
plane, the result being a total loss of sensitiveness. 
13. Radiometer. — A two-disk, cup-shaped, aluminium radiometer, facing 
opposite ways ; both sides bright. Exposed to a standard candle 3^5 inches 
off, the fly rotates continuously at the rate of one revolution in 3.37 seconds. 
A screen placed in front so as to let the light shine only on the convex surface, 
produces repulsion of the latter, causing continuous rotation at the rate of 
one revolution in 7^5 seconds. When the convex side is screened off, so 
as to let the light shine only on the concave, continuous rotation is produced 
at the rate of one revolution in 6-95 seconds, the concave side being 
apparently attradled. These experiments show that the repulsive adtion of 
radiation on the convex side is about equal to the attradlive adtion of 
radiation on the concave side, and that the double speed with which the fly 
moves when no screen is interposed is the sum of the attradlive and re- 
pulsive adtions. 
14. Radiometer. — A two-disk, cup-shaped, aluminium radiometer, lamp- 
blacked on the concave surfaces. In this instrument the usual adtion of light 
is reversed, rotation taking place, the bright convex side being repelled, and 
the black concave attradled. When the light shines only on the bright 
convex side, no movement is produced, but when it shines on the black con- 
cave side, this is attradled, producing rotation. 
15. Radiometer. — A cup-shaped radiometer similar to the above, but having 
the convex surfaces black and the concave bright. Light shining on this 
instrument causes it to rotate rapidly, the convex black being repelled. No 
movement is produced on letting the light shine on the bright concave sur- 
face, but good rotation is produced when only the black convex surface is 
illuminated. 
16. Radiometer. — A multiple-disk, cup-shaped, turbine radiometer, bright 
on both sides, working by the adtion of warm water below and the cooling 
effedt of the air above. 
17. Radiometer. — A four-armed metallic radiometer with deep cups, bright 
on both sides. 
18. Radiometer. — A four-armed radiometer, the vanes consisting of mica 
cups, bright on both sides. 
19. Radiometer. — A four-armed radiometer, having clear mica vanes. The 
diredtion of motion being determined by the angle formed by the mica vanes 
with the inner surface of the glass bulb. 
An important improvement in the produdtion of the eledtric light has 
