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POPULAR SCIENCE REVIEW. 
based on the fact that the light of Venus is so strong that objects placed in 
it cast a well-defined shadow. (Mr. Plummer somewhat strangely says that 
Venus is frequently bright enough to cast a well-defined shadow !) “ The 
plan I have adopted,” he says, “ has been to compare the light of the planet 
with that of a standard sperm-candle burning 120 grains of wax per hour, 
and to vary the distance of this until the shadow it casts upon a screen of 
white paper has an equal degree of intensity to that given by the planet. It 
being found impossible to get the two shadows on the same screen, separate 
screens were arranged for each, and brought as near to each other as possible. 
The arrangement was therefore a modification of Rumford’s photometer. 
The objects of which the shadows were observed were two equal cylindrical 
steel wires of i-inch diameter, placed in a dark room, nine feet in front of 
their respective screens ; but the judgment was further assisted by noting also 
the shadows of the wooden laths to which the wires were attached, and of 
which the thickness was about £ inch. These conditions were preserved 
throughout the whole of the observations. To protect the candle from 
wind, it being necessarily placed in the open air, it was fixed within a lantern, 
which was itself enclosed, except upon one side, in a rough wooden box, 
painted a dull black. These precautions are believed to have been sufficient 
for their purpose.” The result of these observations is to assign to Venus 
at her greatest brilliancy almost exactly one-800th part of the light of 
the full moon. As Bond’s observations assign to Jupiter at mean opposition 
one-6430th of the light of the full moon, andTo Venus at her greatest brilliancy 
4*864 times the brightness of Jupiter, it follows that Mr. Plummer’s estimate 
of the brightness of Venus exceeds by about 65 per cent, the estimate 
deducible from Bond’s observations (one-1322nd part of the light of the full 
moon). Mr. Plummer considers that “ since the meihods employed are en- 
tirely dissimilar, and since Bond’s investigation has chiefly to do with the 
moon and Jupiter, both of which Bond observed at altitudes generally much 
greater than that at which the observation of Venus is possible, this discord- 
ance does not prove much.” Perhaps not ; but, in our judgment, it disproves 
a good deal. 
Proper Motion of Bright Spots on Jupiter. — Mr. Brett has observed 
that some spots on Jupiter during the late opposition were affected by 
a considerable proper motion. As these observations required only a good 
eye for position, reliance can in all probability be placed upon them. Mr. 
Brett has not corrected his computation for the effects of the planet’s retro- 
grade motion ; taking that into account, the spots observed would seem to 
have travelled at a rate of fully 150 miles per hour. This is not quite so 
great as the proper motion of a rift observed by Baxendell of Manchester, 
one end of which travelled at a rate of 190 miles per hour for a period of 
at least six weeks. The spots observed by Mr. Brett were judged by him 
to be 6,000 miles in diameter, and from the character of their shading and 
shadows he regarded them as globular in form — an opinion which will 
probably not be accepted unless stronger evidence can be advanced in its 
favour. 
The Bings of Saturn. — Mr. Trouvelot, of the Harvard Observatory, Cam- 
bridge, Mass., has made some interesting observations upon the rings of 
Saturn. From these it appears that the rings present all those character- 
