SCIENTIFIC SUMMARY. 
309 
-definition. Many photographs, which to the eye appeared good, lost all 
strength and sharpness when placed under the measuring microscope. It 
was once remarked to me, 1 you might as well try to measure the Zodiacal 
light.’ A final result, 8*17 ", was obtained from Mr. Burton’s measures, and 
8*08" from Captain Tupman’s.” These values correspond to mean solar dis- 
tances of 100,050,000 miles and 101,104,000 miles, which are of course 
utterly untenable. 
The Transit of Mercury . — The weather on May 0 was not favourable in 
this country or in France. The contacts were observed at Gottingen, 
■ Josephstadt, Kiel, Antwerp, San Fernando, and Christiania. At Kiel and 
San Fernando a difference of time was noted between apparent and real 
•contact *, elsewhere none seems to have been noted. In the United States 
many important observations were made, both by American astronomers 
and the French Expedition. We learn that at the observatory of Dr. Henry 
Draper, Hastings, on the Hudson, a number of observers availed themselves 
of the admirable instrumental resources provided by Dr. Draper, and the 
weather being favourable very good results were obtained ; several of the 
negatives taken by Dr. Draper were particularly good. Observations were 
made also at Washington by Professor Newcomb ; and at other established 
astronomical observatories. The mean time of first internal contact reduced 
to the earth’s centre was in every case earlier than the calculated time by 
•an interval varying from 14T seconds at Washington to 37 *7 seconds at 
•Gottingen. 
Physical Phenomena Observed at the Transit of Mercury . — The bright spot 
was seen by several observers, and not seen by about as many more. If 
those who saw it had all seen the same spot, the positive would overweigh the 
negative : but this was by no means the case. Some saw the spot in the 
middle of Mercury’s disc, some saw it eccentrically situated ; to some it 
appeared as a well defined point, to others as a misty patch ; to some single, 
to others double. Remembering further the utter improbability, we may 
.almost say the physical impossibility, that there could really be present on 
the surface of Mercury a spot bright enough to be seen under the circum- 
stances in which a transit is observed, we cannot hesitate to regard the spot 
as a merely optical phenomenon. As to the ring around Mercury the case 
seems almost as clear, but not quite so. On any physical interpretation of a 
ring either dark or bright seen round Mercury, a bright arc should be dis- 
tinctly visible round the part of Mercury not yet entered on the sun before 
first internal contact, and round the part which has passed outside the solar 
disc after second internal contact. Nothing of the sort seems to have been 
noticed on May 6. If when all the accounts, and especially those from 
America, have been received, this should turn out to be the case, we must 
reject the observations of a ring seen round the planet when on the sun, as 
unquestionably illusory or optical phenomena only. That this is so, is 
strongly suggested by the varying nature of the phenomena seen by different 
observers. Some saw a bright ring, others a dark one ; some a broad ring 
round a narrow one : the bright ring was uniform as seen by some, a mere 
bright border to a dusky ring, as seen by others ; complete as seen by most 
observers, incomplete as seen by one observer. On the whole, it seems 
tolerably certain that the ring is an entirely subjective phenomenon, and 
