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POPULAR SCIENCE REVIEW. 
mical world to suspect. Lieutenant Herscliel, at liis father’s request, has 
carefully examined the nebula with the five-inch telescope (refracting), 
supplied by the Eoyal Society for the eclipse-observations. From his 
drawings it appears that the stars in the nebula have not shifted their places, 
and that the nebula itself, so far as can be judged from the comparison 
between views taken with an 18-inch reflector and with a 5-inch refractor, 
has a shape now very much resembling that which it had when Sir John 
Ilerschel was at the Cape. It is brighter, or seems to be so j but the change 
may partly be ascribed to the change of v Argus (around which the nebula 
clings) from the first to the sixth magnitude. 
Method of viewing the Solar Prominences without an Eclipse. — It is an- 
nounced that Mr. Huggins has been successful in applying means to render 
the solar prominences visible when the sun is not eclipsed. If it should 
appear that the method is one which may become generally available, this 
discovery will be undoubtedly of extreme importance. Nothing seems now 
wanting for the determination of the exact nature and purpose of these sin- 
gular objects except the means of watching the processes of change which 
they may be undergoing. 
The Nehidar Hypothesis of Laplace. — Professor Kirkwood, of America, 
has discovered some very singular relations in (1) the asteroidal system, and 
(2) the system of rings and satellites circling around Saturn. He takes a 
list of 97 asteroids, and having arranged them in the order of their dis- 
tances, he examines those instances in which the gap between successive 
distances is considerably in excess of the mean interval. He finds that in 
every instance the gap corresponds to a mean distance such that an asteroid 
revolving at that distance would have a period commensurable with that of 
Jupiter. Thus, having first taken the 72 nearer asteroids (because the 
remoter, as more difficult of detection, require to be placed in a class by 
themselves), he finds that the mean interval between the first and the last 
of this set is 0-0081. The greatest gap in the order of distances occurs 
between Ariadne and Feronia, whose mean distances are respectively 2-2034 
and 2-2G54 — so that the interval 0-0620 is nearly eight times the mean. 
Now a planet having a period equal to two-sevenths that of Jupiter would 
have a mean distance of 2 -2569, which it will be seen lies between the two 
values given above. Again, the interval between the mean distance of 
Thetis (2-4737) and that of Hestia (2-5178) is 0-0441, or more than five 
times the mean ; and a planet having a period equal to one-third that of 
Jupiter would travel at a mean distance of 2-5012. In the outer section, 
the mean interval is 0-0286. The greatest hiatus occurs between the mean 
di.stances of Undina and Freia (3-1917 and 3-3877), the breadth being 
0-1960, or more than eight times the mean. A planet having a period equal 
to one-half that of Jupiter would revolve at a mean distance of 3-2776. 
And one or two other similar coincidences are noted. Undoubtedly this 
result is well worthy of notice ; and if these researches should be confirmed 
when the number of known asteroids is very much increased, they would 
seem to point to a physical cause as the only possible explanation. As it 
is, the doctrine of chances is largely in favour of Ih-ofessor Kirkwood’s view 
th.at such a cause has been in operation. He points to the efiect of com- 
mensurability of the sort considered, in causing disturbances in the motion 
