SCIENTIFIC SUMMARY. 
197 
the question naturally arises, how is the longer time which development 
may probably suggest to be obtained. Will the sun and moon stand still to 
oblige Mr. Joseph Lockyer, as it once did, w’e are told, to help Joshua P 
May we be permitted to recall an experience of the eclipse of 1871 ? On 
that occasion an enthusiastic observer, having collected for his own use all 
the best instruments, rushed during totality from one observation to another 
(he called these “strategic movements,” however), endeavouring during the 
two minutes of totality to make nine distinct observations. The sun and 
moon not standing still, he naturally missed the whole set. Is it too much 
to say, that unless Dr. Schuster and his assistants wisely take the matter into 
their own hands on the present occasion, the Royal Society expedition runs 
great risk of failure similarly complete P 
Fortunately the Indian Government may be expected to send observers 
who will take some good photographs of the corona, while Davis, the skil- 
ful photographer of Lord Lindsay’s party, will probably achieve even better 
results. 
Periodicity in the Value of the Sun’s Diameter . — In the report of the Astro- 
nomical Society the following occurs : “ The question whether the sun’s ap- 
parent diameter is liable to periodic changes has frequently occupied the 
attention of astronomers. The subject has been investigated by Von Lin- 
denau, Bessel, and Bianchi, and more recently by Le Verrier, Secchi, Wagner, 
and Auwers. Lindenau was led to the conclusion, by a discussion of the 
Greenwich observations from 1750 to 1755, and from 1765 to 1786, that the 
sun is an ellipsoid, with a compression of to Bianchi, apparently 
without being acquainted with Lindenau’s research, found the solar compres- 
sion gloj but by changing his method of investigation he obtained values 
for this quantity varying from l9 ~ to Bessel, however, considered that 
a progressive shifting of the wire-frame of the Greenwich transit-instrument 
would account for the apparent periodicity in the values of the solar di- 
ameter. M. Le Verrier, after a careful investigation, came to the conclusion 
that no real periodic variation in the sun’s diameter existed equal to 0 s -02. 
More recently, Padre Secchi, considering that the active forces known to be 
in progress on the surface of the sun might very possibly produce changes 
in the volume of the luminous matter composing the chromosphere, an- 
nounced the result of some researches on which he had been engaged in 
conjunction with Padre Rosa. He concluded that the variations in the solar 
diameter were the most apparent when the activity of the forces on the sur- 
face of the 4 sun was greatest; and he considered that, as these variations 
were frequently more than 3" in amount, they could not be accounted for 
by mere errors of observation. Dr. Auwers, however, who has since tho- 
roughly examined the methods adopted by Padre Secchi, gives as his opinion 
that the foundations of the theory employed by the latter are so unreliable 
that, for the present, these results cannot safely have much weight attached 
to them. Dr. Auwers, anxious to have an independent series of observations 
as the basis of his examination, obtained from the Observatories of Green- 
wich, Oxford, Paris, Brussels, Washington, Konigsberg, and Neuchatel, a 
large number of measures of the solar diameter observed during the same 
period as those by Padre Secchi at Rome. 
“ With regard to the connection of the value of the sun’s diameter with 
