SCIENTIFIC SUMMARY. 
91 
solar heat due to sunspots, amounts to one-tenth per cent, of the whole 
radiation (whose thermometric effect registered here is a change of at least 
70° C.) : whence we find 0°*063 C., as the least change in terrestrial tem- 
perature which we can attribute to the direct action of the spots ; and the 
greatest change in terrestrial temperature which can be due to this cause 
amounts to 0 o, 29 C. Thus “ sunspots ” do exercise a direct and real in- 
fluence on terrestrial climates by decreasing the mean temperature of this 
planet at their maximum, but the decrease is so minute that it is doubtful 
whether it has been directly observed or discriminated from other changes.” 
Equatorial Motion loith an Altazimuth Stand. — Lord Lindsay describes a 
method of making an ordinary altazimuth telescope follow a celestial body 
along a parallel of declination, which many who have used an altazimuth in 
astronomical observation must have thought of. It is manifest that when a 
telescope is sweeping a declination parallel, a point of the tube lying on a 
line drawn parallel to the collimating axis through the intersection of the 
horizontal and vertical axes, must travel in a circle having its plane parallel 
to the equator and its centre on the polar axis through the last named point 
of intersection. Its distance, therefore, from any point on this polar axis 
must remain unchanged. If then such a point of the tube be connected 
with a fixed point lying on this polar axis, the telescope will sweep a decli- 
nation-parallel, if turned around the vertical axis in such sort that the 
connecting string remains stretched. As the length of the connecting 
string can be readily altered, the telescope can be made by this arrange- 
ment to sweep out any declination-circle. The idea is not a new one. It 
was long ago suggested by Sir G-. Airy, with, however, a somewhat incon- 
venient arrangement, the fastening string being attached above and behind 
(or north of) the pivot. Lord Lindsay suggests a string attached in front 
(or south) of the pivot j in fact, from a point on the tube near the object- 
glass to a fixed point suitably placed due south of the vertical axis. In the 
illustration accompanying Lord Lindsay’s paper the point near the object- 
glass is not correctly placed ; it is on the tube itself, whereas the pivot (or 
intersection of the axes of motion) is about 1^ inch from the tube. 
The Planet Vulcan. — Some excitement was occasioned among the be- 
lievers in Vulcan by the announcement that in April last M. Weber, at 
Petcheli had seen a round spot on the sun, which a few hours later had 
vanished. After Wolfe, Leverrier, Moigno, and others, had expressed their 
conviction that this was a real transit of Vulcan, and had urged astronomers 
to look out for another transit in October, it was discovered that Weber’s 
spot had been seen at the Madrid Observatory, and had been photographed 
at Greenwich. It was seen, however, and photographed as an unmis- 
takable sunspot, and Weber’s view of it as a round black disc which might 
have been a planet in transit, was due simply to the small power of his 
telescope. We wonder how many reported u transits of Vulcan” would thus 
have been explained away if a systematic observation of sunspots had been 
made in former years as at present P 
Total Eclipse of the Moon, partly visible at Greenwich. — On the evening of 
Peb. 27, the moon will rise at Greenwich already partly obscured by the 
earth’s penumbra, but the true shadow wdll not encroach upon the moon’s 
disc until 1^ min. later, or at 29^ min. past 5, p.m. Total phase will begin 
