SCIENTIFIC SUMMARY. 
179 
As the cabsolute time of each phenomenon would require to be known, 
this method would not be available unless the longitude of each place of 
observation were known within a second or so. It is on this account that 
the Astronomer Koyal calls the attention of men of science to the necessity 
of preparing for the coming transits by carefully ascertaining the longitudes 
of places suitable for the proposed observations. 
Observation of the Transits of Venus by means of Photography. — Mr. Warren 
De la Rue, at the desire of the Astronomer Royal, has placed before the Astro- 
nomical Society a statement of the means by which photographic views of 
the sun taken at different places during the course of the transit, might be 
rendered available for the determination of the sun’s distance. What would be 
required would be— 1, the determination of the epoch of each photographic 
record ; 2, proper corrections of the photographs for optical distortion ; and 
3, corrections (if experiment should suggest any) for shrinkage of the 
collodion. Mr. De la Rue proposes that six precisely similar instruments 
should be prepared and mounted equatorially, but without circles or driving 
clock, and sent to six convenient stations. The optical distortion of each 
instrument could be determined beforehand, and no further experiment 
would be necessary, as all the parts would be rigidly fixed. 
Major Tennant's Photographs of the Great Eclipse . — For several months 
after the receipt of Major Tennant’s telegram from India, announcing that 
six photographs of the sun had been taken, the scientific world had con- 
tinued in suspense respecting their value. Major Tennants letters had 
indeed rather tended to convey the notion that the photograph.s were com- 
parative failures, than that he had been completely successful. It was, 
therefore, a pleasing surprise when, at a recent meeting of the Royal Astro- 
nomical Society, Mr. De la Rue announced that the photographs were 
eminently valuable and interesting. After all the care and expense devoted 
to the preparation of the expedition, and the skill with which Mr. Browning 
had overcome the difficulties attending the construction of the 9-inch New- 
tonian for photographing, it would have been a matter for regret had the 
expedition been rewarded with anything but complete success. We shall 
await the publication of trustworthy copies of the photographs taken at 
Aden before considering Major Tennant’s photographs at length. One im- 
portant point will probably be settled by the comparison of the two sets of 
photographs. From direct observations of a great pointed prominence which 
attracted the attention of nearly all the observers of the eclipse, it appears 
probable that during the interval between the earlier and later views, this 
prominence underwent remarkable changes of figure. As it is depicted 
in Major Tennant’s photographs as an enormous spiral with convolutions 
diminishing in range from base to summit, it seems likely that processes of 
a remarkable character were at work at this part of the sun’s surface. As 
Aden and Guntoor are so far apart, there is every reason for hoping that the 
indications of change will be sufficiently marked when the two sets of 
photographs are compared. Indeed, from a drawing in the Engmeery 
which purports to represent the aspect of this prominence as seen at Aden, 
it seems tolerably clear that such a change had taken place. 
The Nebula in Argo. — It appears that, after all, there have been no such 
changes in this nebula as Mr. Abbott’s communication had led the astrono- 
