94 REPORT—1850. 
hand, it may happen that the two stars are really as well as seerningly near, and may 
act upon one another by their mutual attractions, after the manner of sun and planet. 
Such stars are called “‘ physically”’ double. 
Nearly a century ago the Kev. John Mitchell attempted to deduce from the theory 
of probabilities, the chances against the fortuitous approximation of two or more 
stars, supposing the stars generally to be ‘‘scattered by mere chance as it might 
happen.”” He concludes that there is a probability of 80 to 1 that the two stars 
8 Capricorni are physically connected, and above 500,000 to 1 that the stars of the 
Pleiades are so. These results have been implicitly adopted by most subsequent 
writers on probabilities and on astronomy. 
The author denies in toto the legitimacy of the influences and the possibility of 
putting a numerical value upon such evidences of physical relation. As inductive 
presumptions of such a connexion, he admits that they have a certain evidence in 
their favour; but one not more expressible by numbers than that of any physical 
theory, such as that of gravity. ‘The author endeavours to show that Mitchell has 
confounded the mere expectation of an event which may or may not occur, with the 
inherent probability that a particular event which has occurred, should happen rather 
than any other possible event. He also shows that Mitchell’s mathematical ex- 
pression of the result of random scattering leads to absurd results, and must there- 
fore be erroneous and delusive. 3 
The following were stated to the meeting as the results at which the author had 
at that time arrived :— 
(1.) The fundamental principle of Mitchell is erroneous. The probability ex- 
pressed by it is an altogether different probability from what he asserts. His cal- 
culations are also apparently inaccurate, in some instances at lcast. 
(2.) All the xumerical deductions of his successors are equally baseless. 
(3.) Were Mitchell’s principle just, a perfectly uniform and symmetrical dispo- 
sition of the stars over the sky would (if possible) be that which could alone afford no 
evidence of causation, or any interference with the laws of ‘random ;”—a result 
palpably absurd. : 
(4.) Special collocations, whether («) distinguished by their symmetry, or (8) 
distinguished by an excessive crowding together of stars, or the reverse, inevitably 
force on the reasoning mind a more or less vague impression of causation ;—an im- 
pression necessarily vague, having nothing absolute, but depending on the previous 
knowledge and habits of thought of the individual, therefore incapable of being made 
the subject of exact (7. 6. mathematical) reasoning. 
On the Distribution of Shooting Stars in the Interplanetary Spaces. 
By Henry Hennessy. 
The attention of the writer having been excited by the periodical return and other 
remarkable circumstances connected with falls of shooting stars, he proceeded to 
examine from the data already obtained, the laws of distribution of these bodies in 
space. Adopting the opinion that these masses circulate either in rings or cloud- 
like bodies around the sun, the possibility that their distribution may be also de- 
pendent on their mean distances from the sun, is brought under consideration. The 
position of the orbits of the known groups of aérolites, and also the comparative 
numbers expressing the amount falling at different parts of the earth’s orbit, would 
assist in determining this point. Astronomers appear in general to agree that these 
groups circulate within the earth’s orbit, and from a calculation made by Kaemtz, 
quoted by Dove*, it seems that the greater proportion of aérolites fall during that 
half of the year when the earth is near its perihelion. It follows therefore that 
shooting stars increase in number in going towards the sun. If this conclusion be 
combined with the views of Colonel Portlock respecting fossil aérolites, as stated at 
the Swansea meeting of the British Association, it would follow that the earth’s mean 
distance from the sun has been undergoing a secular diminution since the earlier 
geological epochs. An interplanetary resisting medium would account for this 
secular inequality, but as observation has not as yet detected it, the truth of the fore- 
* Repertorium der Physik, 1841. 
