194 
POPULAR SCIENCE REVIEW. 
place in the temperature of the air near the ground. This occurs at the 
period of lunation when the moon has acquired the greatest amount of heat 
it can receive from the sun, which is when the half-moon then illuminated 
has been subjected to solar radiation for about 265 hours, or at the third or 
last quarter. Precisely opposite results will occur at the time of minimum 
heat in the moon. We have heard of experiments to test the heat given out 
by the full moon and, if we mistake not, it was Professor C. P. Smyth, in 
his Teneriffe experiment, who found that it was so little as not to amount 
to more than would be given by a wax candle at the distance of fifteen yards. 
Mr. Harrison shows us that this was not the right time to expect to discover 
heat from our satellite ; the fact being also that, at the time when most heat 
was really given out, the effect upon the earth’s surface was that a lowering 
of the temperature was produced. In confirmation of what was stated, Mr. 
Harrison showed the tabulated results of temperature at Oxford, Greeuvrich, 
and Berlin, taken for several years at each place, which agreed in proving 
that, at the time when by calculation the moon must have acquired the 
greatest heat, the average temperature on the earth's surface was lower, 
accompanied by a dispersion of cloud. 
Zarffe Telescopes. — In our January number we mentioned the completion 
of the large object-glass of 25 inches diameter, which Messrs. Cooke had 
been grinding for Mr. Newall. The equatorial mounting for this immense 
glass, which weighs, we believe, without its cell, no less than 146 lbs., is 
now complete, and it is expected that the instrument will, during the pre- 
sent year, reach Madeira, where it is to be erected and placed under the 
superintendence of Mr. Marth, whose familiarity with large telescopes, gained 
while at Malta with Mr. Lassell, is a guarantee that the new instrument will 
be in competent hands. Mr. Newall will complete the establishment by the 
addition of a 7-inch transit circle. The gTeat reflector, by Mr. Grubb of 
Dublin, now in course of manufacture for the Melbourne Observatory, also 
approaches completion, and, both in optical definition and mechanical ar- 
rangements, is all that can be desired. The speculum is 4 feet in diameter ; 
the driving clock does its work with the greatest precision, and the neces- 
sary apparatus for photography and spectroscopic examination is to be 
added to the instrument. The means of sheltering the telescope from rain 
and dust are not yet definitely settled, but a dome of 46 feet diameter is 
suggested. 
Suspected Change in one of the NebulcB.—The Eev. H. Cooper Key has been 
making a series of observations on the planetary nebula, 45 Herschel, iv. 
Geminorum, with a silvered glass speculum of 18 inch aperture, and 10 feet 
focal length, vsing an eye-piece giving a power of 510. This object pre- 
sented! to the Herschels a uniform nebulous disc with a stellar centre, but 
no ring ; Lord Rosse saw one ring only ; in Mr. Key’s telescope two rings were 
distinctly visible. Mr. Huggins considers the observation important as show- 
ing a definite change in these objects; the central star of the nebula gives a 
continuous spectrum, and possibly the luminous haze surrounding it also, but 
of that Mr. Huggins is not so certain, the difiiculty of getting spectrum ob- 
servations of these faint objects being so great. 
The\Lunar Crater Linne has been diligently observed by the Rev. T. W. 
Webb during the last few months. On the 3rd of February, during an 
