6 REPORT—1863. 
with one hand we slightly move the telescope the image of the star changes its 
position ; and during that motion, on account of the persistence of sensation on the 
retina, instead of appearing like a spot, it assumes the shape of a continuous line. 
Now if, instead of moving the telescope in a straight line, we endeavour to move 
it in a circular direction, the star appears like a circle, but very irregular, on ac- 
count of the unsteadiness of the movement communicated by the hand. Such is 
the principle of the instrument employed by the author to communicate the perfect 
circular motion, which it is impossible to impart by the hand. The instrument 
consists of a conical tube placed horizontally on a stand, and revolving on its own 
axis by means of wheels; inside this tube a telescope or an opera-glass is placed, 
by which, by means of two opposite screws, the end of the object-glass can be 
placed in an excentric position in various degrees according to the effect desired, 
while the eye-glass remains in the centre of the small end of the tube, Now, 
we understand that when the machine makes the tube revolve upon its axis, the 
telescope inside revolves in an excentric direction, and during the revolution the star 
seen through it must appear like a circle. This circle exhibits on its periphery the 
various rays emitted by the star, all following each other in spaces corresponding 
with their duration, showing also blank spaces between two contiguous rays which 
must correspond with the black lines of ee spectrum. The instrument, in fact, is 
a kind of spectroscope, by which we can analyse the light of any star, study the 
cause of the scintillation, and compare its intensity in various climates or seasons 
and at different altitudes. 
On the Relationship between the Variation of the Excentricity of the Earth’s 
Orbit and the Moon’s Mean Motion in Longitude. By the Rev. Dr. E. Hincxs. 
One of the hieroglyphic inscriptions at Thebes contains a notice of an eclipse of 
the sun, observed on a given day of a given year of a certain king; but according 
to Hansen’s tables, no eclipse could have been visible on that day so far west as 
Thebes. Dr. Hincks therefore asked for the assistance of those more practically 
engaged than himself in astronomical pursuits in answering the following queries : 
—Let e, and M, be the excentricity of the earth’s orbit and the mean longitude of 
the moon at the beginning of 1801. Let e,, and M, be the excentricity and the 
mean longitude at the end of any time 7, the longitude being reckoned from the 
equinox of 1801. 
Let e,=e,+e,T+e,T* 
and M,,=M,+M,rt+M,1?+M,1°*. 
It was formerly thought that M,=ae, and M,=a,e,; a and a, being coefficients 
supposed to be known. Some years ago it was discovered that these coefficients 
were much less than they had been supposed to be; and it was inferred that some 
other cause had combined with gravity to make M, so great as it is. Within the 
last year he had heard that some eminent astronomers were of opinion that e, was 
‘much greater” than it had been supposed to be; but he had heard nothing pre- 
cise as to its value. It had occurred to him that as M, had been greatly overrated 
by astronomers, the above equation M,=ae, might still hold good. If so, the 
eclipse might not only be visible at Thebes, but annular ; and it was more probable 
that a recorded eclipse should be of an unusual character, as an annular eclipse 
would be, than an ordinary partial one. The moon being near her apogee, a total 
eclipse would be impossible. On the possibility of the equation raune good, he 
desired to ascertain the opinions of the Section. 
Description of a Solar Eyepiece invented by the Rev. W. R, Dawzs, F.RAS., 
and constructed, under his direction, by Dottonn. Communicated by Dr. Lux. 
In the greatly improved form of this eyepiece, as exhibited, the fundamental 
principle of the original construction is preserved, which consists in greatly con- 
tracting the field of view, so that the heat emanating from the portion of the sun’s 
focal image admitted to the eye-glass, however large the telescope may be, shall 
be less than would cause any injury to the dark glasses which defend the eye from 
excessive light. The diaphragms by which the field is thus contracted are arranged 
— 
ee 
