395 
83,000; and six months afterwards 65,000 - 18,000=47,000 miles an hour 
only. Is this credible on physical principles ? Moreover, if the sun’s motion 
in space were 65,000 miles an hour (Bessel thought it twice or three times as 
great), then the earth’s orbital motion once a year would momentarily cease ; 
as it must then describe a perfect cycloid in going round the sun. Then its 
velocity once a year would be 65,000+65,000=130,000 miles an hour ; and 
six months afterwards, 65,000 — 65,000=0, according to well-known mecha- 
nical principles and the necessities of the laws of space and motion. It is 
not so plainly obvious, but it is equally true, that if the sun’s motion is 
only 18,000 miles an hour, the earth must yearly pause altogether for an 
instant, in describing the looped curve it must describe in going round the 
sun This is a mere fact of mechanical construction ; the earth’s path 
would be what I nrny call a compressed cycloid. But is that credible ? ” — 
( Astronomical Register , February, 1864, p. 38.) 
29. Well, to this an orthodox” astronomer actually 
ventured to reply, in the following number of the Astronomical 
Register , with the initial “D.”; and I am informed the writer 
is a Mr. Dell, of Aylesbury. He wrote as follows : — 
“ (1.) In the February number of the Register, there is a letter from 
Mr. Reddie on the subject of the Motion of the Solar System in 
Space, in which he asserts that there can be no such motion, because of 
some fanciful contradictions ‘ to well-known mechanical principles ’ ! 
“ (2.) I presume it will be admitted that Jupiter with his satellites is 
strictly analogous to the solar system, on a small scale ; and we can therefore 
bring Mr. Reddie’s assertion to the test of observation. 
“ (3.) Substituting Jupiter for the Sun in the following paragraph of the 
letter referred to, we shall read , — 1 If Jupiter moves in space, the variations 
iu the orbital velocities of all the bodies that revolve about it must differ by 
the whole amount of J upiter’s motion, when at right angles to its path, twice 
in every revolution they make.’ For instance, taking Jupiter's motion at 
29,000 miles an hour, the second satellite’s mean orbital velocity of 32,000 
miles an hour must sometimes be 32,000 + 29,000 = 61,000, and half a 
revolution afterwards, 32,000 — 29,000 = 3,000 miles an hour only. 
“ (4.) Now when Jupiter is in opposition, these two points of maximum 
and minimum velocities will occur at the occultation and transit of the 
satellites. For instance, taking the second satellite, its velocity at its 
occultation should be, according to Mr. Reddie, 61,000 miles an hour, it 
being then moving at a right angle with the planet’s path, and in the same 
direction ; while at its transit it should have a velocity of 3,000 miles an 
hour only, as it will be moving at a right angle to its primary’s path, but in 
an opposite direction. Therefore the time occupied by the transit of the 
satellite should be somewhere about twenty times that occupied by the 
occultation. 
“ (5.) But according to observations at previous oppositions, and to the 
