Nov. 30, 1882 | 
NATURE 
117 
that the Germans have published anything official on the subject; 
but the English official report has appeared, and it frankly 
declares that ‘‘ after laborious measures and calculations it was 
thought best to abstain from publishing the results of the 
photographic measures as comparable with those deduced from 
telescopic view.” From the way in which these photographs 
were taken, Sir George Airy saw that they could not yield 
position angles of any value, and therefore differences of rizht 
ascension and declination could not be determined from them ; 
but they did seem capable of giving the distance between the 
centres of Venus and the sun with considerable accuracy. Upon 
trial this proved not to be the case. No two persons could 
measure them alike, because ‘‘ however well the sun’s limb on 
the photograph appeared to the naked eye to be defined, yet on 
applying to it a microscope it became indistinct and untraceable, 
and when the sharp wire of the micrometer was placed on it, it 
entirely disappeared.” In short, the British photographs aro 
useless for the present, but Sir George Airy hopes that in the 
future some astronomer may be found who will be capable of 
dealing with them. 
We turn now to the American photographs, They present a 
well defined image of the sun about 4.4 inches in diameter, and 
are intended to give both the position angle and distance of 
Venus from the sun’s centre. A special engine was at hand for 
measuring them, but when they were placed under the microscope 
only an indistinct blur could be seen, Here again was the sa ue 
difficulty which had baffled the English, but fortunately its 
cause was soon discovered. The magnifying power of the 
microscope was only 374 diameters, which seemed moderate 
enough, but was it really so? The photographic image of 
the sun was about 4.4 inches in diameter, and this was magnified 
3.31 times by the objective of the microscope, thus giving an 
image 14.56 inchesin diameter. To yield an image of the same 
size, a telescopic objective would require a focus of about 1563 
inches, and if the eye-piece of the microscope, which had an 
equivalent focus of 0.886 of an inch, were applied to it, a power 
of 1764 diameters would be produced. This then was the 
utterly preposterous power under which the image of the sun 
was seen when the photograph was viewed through the micros- 
cope, and no useful result could be expected from it. Means 
were immediately provided for reducing the power of the 
microscope to 5.41 diameters, and then the photograph seen 
through it appeared as the sun does when viewed through a 
telescope magnifying 255 diameters. After this change all 
difficulty vanished, and the photographs yielded excellent results. 
The measurements made upon them seem free from both constant 
and systematic errors, and the probable accidental error of a 
position of Venus depending upon two sets of readings made 
upon a single photograph is only 0.553 of a second of arc. To 
prevent misunderstanding it should be remarked that this state- 
ment applies only to pictures taken between second and third 
contact, and showing the entire sun, The small photographs 
taken between first and second contact and again between third 
and fourth contact, proved of no value. 
These investigations consumed much time, and before the 
result from the American photographs was generally known, an 
international convention of astronomers was held in Paris to 
consider how the transit of 1882 should be observed. The 
United States was not represented at this conference, and 
guided only by their own experience, the European astronomers 
declared that photography was a failure and should not be tried 
again. They knew that the contact methods are attended by 
difficulties which have hitherto proved insurmountable, but under 
the merciless pressure of necessity, they decided to try them 
once more. Unfettered by the action of the Paris Conference, 
the United States Transit of Venus Commission took a very 
different view of the case. Its members knew that the probable 
error of a contact observation is 0.15 of a second of arc, that 
there may always be a doubt as to the phase observed, and that 
a passing cloud may cause the loss of the transit. They also 
knew that the photographic method cannot be defeated by 
passing clouds, is not liable to any uncertainty of interpretation, 
seems to be free from systematic errors, and is so accurate that 
the result from a single negative has a probable error of only 
0.55 of a second of arc. If the sun is visible for so much as 
six minutes between the second and third contacts, by using dry 
plates thirty-six negatives can be taken, and they will give as 
accurate a result as the observation of both internal contacts. 
These were the reasons which led the American Commission to 
regard photography as the most hopeful means of observation, 
_of the most important astronomical events of the century. 
and thas it happens that the astronomers of the old and new 
worlds differ radicaliy respecting the best means of utilizing one 
The 
Europeans condemn photography, and trust only to contacts and 
heliometers ; the Americans observe contacts because it costs 
nothing to do s», but look to photography for the most valuable 
results 
In 1716, Halley thought that by the application of his method 
to the transit of 1761, the solar parallax could certainly be a 
de‘ermined within the five hundredth part of its whole amount. 
Since then, three transits have come and gone, and the contact 
methods have failed to give half that accuracy. From the 
photographic method, as developed by the U. S. Transit of 
Venus Commission, we hope better things, and perhaps fifty 
years hence its results may be ‘regarded as the most valuable 
of the present transit season. In 1874, as in 1761, exaggerated 
views prevailed respecting the value of transits of Venus, but 
no competent authority now supposes that the solar parallax can 
be settled by them alone. The masses of the Earth and Moon, 
the moon’s parallactic inequality, the lunar equation of the earth, 
the constants of nutationand aberration, the velocity of light, 
and the light equation, must all be taken into account in 
determining the solar parallax, and it cannot be regarded as 
exactly known until the results obtained from trigonometrical, 
gravitational, and phototachymetrical methods are in perfect 
harmony. It may be be many years before this is attained, but 
meanwhile practical astronomy is not suffering. Its use of the 
solar parallax is mainly confined to the reduction of observations 
made at the surface of the earth to what they would have been 
if made at the Earth’s centre ; and for that, our present know- 
ledgesuffices. The real argument for expending so much money 
upon transits of Venus is that being an important factor in 
determining the solar parallax, their extreme rarity renders it 
unpardonable to neglect any opportunity of observing them, 
Let us do our whole duty in this matter that posterity may 
benefit by it, even as we have benefited by the labours of our 
predecessors. 
UNIVERSITY AND EDUCATIONAL 
INTELLIGENCE 
OxrorD.—The professoriate has been strengthened by the 
election of Dr. Burdon Sanderson to the new Chair of Physio- 
logy on the Waynflete foundation in connection with Magdalen 
College. The Biological side of ithe Museum will now be 
divided into two departments, 
The Brakenbury Natural Science Scholarship at Balliol Col- 
lege has been awarded by the Examiners to Mr. Walker 
Overend, of the Yorkshire College of Science and St. Bar- 
tholomew’s Hospital. 
CAMBRIDGE.—Messrs. J. W. Hicks and F. Darwin are 
appointed members of the Botanic Garden Syndicate; Dr. 
Ferrers (Master of Caius), and Prof. Stuart, of the Museums 
and Lecture-Rooms Syn licate ; Prof. Stuart is also specially re- 
appointed to the Local Examinations and Lectures Syndicate ; 
Dr. Ferrers and Mr, Routh are appointed on the Observatory 
Syndicate ; Prof. Humphry and Mr. Vines, on the State Medi- 
cine Syndicate; Mr. Trotter, on the Special Board for Medi- 
cine; Mr. Besant, on the Special Board for Mathematics; Mr. 
Shaw, on the Special Board for Physics and Chemistry; Mr. 
Vines, on the Special Board for Biology and Geology. 
Messrs. J. C. Saunders and J. W. Hicks are approved as 
Teachers of Botany and Chemistry respectively for the purpose 
of certificates for Medical Students. 
The following colleges have offered open exhibitions or 
scholarships for natural science, with examinations in December 
or January next: ‘Trinity, examination, December 12, one 
exhibition of 50/. for two years; candidates to be under nine- 
teen on March 25 next. St, Johns, one exhibition, 50/., for 
three years, examination December 12 ; Caius, Jan. 8; Christ’s, 
Emmanuel, and Sidney, January 12, a joint examination; candi- 
dates for all these must be under nineteen years of age. Parti- 
culars may be obtained from the tutors of the respective colleges. 
GLAsGow,—The following appointments to Scholarships, &c., 
have been made in accordance with the results of the Competi- 
tive Examinations :—George A. Clark Scholarship in Mental 
Philosophy (£200 for four years), John S. McKenzie, M.A. ; 
William Ewing Fellowship in Mental Philosophy (£80 for three 
years), James A. McCallum, M.A. ; Eglinton Fellowship in 
