SCIENTIFIC SUMMARY. 
227 
sented to the Academy of Sciences of Berlin, has obtained a formula which 
(from four years’ observations) expresses the law for the dependence of the 
period of the sun’s rotation on the latitude 
£=16°-8475 — 3*°3812 sin (41° 13' + Heliographic latitude), 
where £ is the angle of rotation in a day. 
M. Delaunay’s memoir deals with the retardation of the earth’s rotation. 
He thinks, as others have thought before him, that the outstanding part 
of the moon’s secular acceleration to which we have before alluded may be 
accounted for by a lengthening of the sidereal day. In spite of Hansen’s 
inquiry into the subject, he considers that, on the hypothesis that the 
disturbing forces of the sun and moon act on the lagging protuberance of the 
great tidal wave, the amount ( of this action is sufficient to produce a 
progressive increase in the time of the earth’s rotation, sufficient to account 
for the outstanding 6" of the moon’s acceleration. On this Mr. Pritchard 
has remarked that, should this hypothesis eventually prove to be correct, 
the scrupulously exact methods of astronomical investigation during the last 
few years will have enabled us to estimate with greater accuracy two of the 
prime elements of the solar system, viz., the mean distance of the sun from 
the earth, and the length of the terrestrial day. Mr. Stone has already 
discussed this paper, and although he bears testimony to its high value, he 
cannot accept the retardation as a demonstrated fact. We believe that, at 
the next meeting of the Astronomical Society, the Astronomer Royal will 
state his opinions on the subject. 
Of planetary observations we have little to record, as none of them are 
well situated for observation with the exception of Saturn, whose rings are 
gradually opening. 
We find in the Monthly Notices for January an interesting paper by 
Mr. Huggins on the variability of the stars, and on some new stars in the 
neighbourhood of the trapezium in the great nebula of Orion. Observations 
of these stars, now that we know something of the nature of nebulae, cannot 
fail to lead to interesting results. In the same number Mr. Brownrig 
describes a very ingenious method of mounting specula and diagonal 
reflectors, on which the maximum of stability is obtained with a minimum 
loss of light. 
At the meeting of the Society in March, Dr. Forster, Hermann Gold- 
schmidt, Mr. Safford, the newly-appointed Director of the Chicago observa- 
tory, and M. Auwers were proposed as associates. 
The Astronomische Nachrichten has recently contained a catalogue of 
double stars observed by Dembowski, of polar nebulae observed by Herr 
Riimker (who was one of the invites at the last meeting of the British 
Association), with a special eye to their proper motion, and a description of 
an ingenious sun eye-piece contrived by Merz. 
We learn from the Bulletin International (which has made its appearance 
in a new shape, with a supplement entirely devoted to astronomical and 
physical novelties) that M. Kaemtz has been appointed Director of the 
Central Physical Observatory of Russia, and that M. Oudemans is doing- 
good work at Batavia, where a magnetical and meteorological observatory — 
we presume on the Kew model — is being erected. The registering thermo- 
meter at this observatory is a copper wire of ten metres in length, stretched 
