76 
POPULAR SCIENCE REYIE'W. 
that an efficient corrective may be obtained by applying a glass prism, of 
small refracting angle, in the eye-piece of the telescope. Flint prisms of 2°, 
4°, 6°, 8°, 12°, and 16° effect the desired correction most satisfactorily. For 
use with the naked eye the prisms of lowest refracting angle must be used 
with the edge downwards ; for view with an inverting telescope the edge 
of the prism must be upwards. The higher the power the larger ( cceteris 
paribus) must be the refracting angle of the prism selected; so also for 
objects very near the horizon a prism of large refracting angle must be 
used. 
Transits of Venus in 1874 and 1882. — Dr. Peters, of Altona, has re-exa- 
mined the circumstances of the transit of 1874. He finds that Mr. Hind’s 
determination of the fundamental elements of the transit are appreciably 
correct. He then enters into a consideration of the conditions for the suc- 
cessful observation of the transit. He points out that Halley’s method will 
be better than Delisle's. In this and other respects his results agree with 
those deduced by Mr. Proctor. He is of opinion, further, that the observa- 
tions made in 1874 will be much more trustworthy than those of 1769. 
Mr. Proctor has applied to the transit of 1882 the same processes by 
means of which he had already calculated the circumstances of the earlier 
transit. The following are the deduced places where ingress and egress are 
most affected by parallax : — 
Lat. Long. 
51° 5' S 86° 48' E. 
53 16 N 94 28 W. 
26 18 N 40 1 W. 
23 46 S 137 11 E. 
(l) The place where first internal con- 
tact is most accelerated lies in 
(ii) The place where first internal con- 
tact is most retarded lies in . 
(iii) The place where last external con- 
tact is most accelerated lies in 
(iv) The place where last internal con- 
tact is most retarded lies in 
He remarks that u the corrections which have to be made in the case of 
this transit are less considerable than those he made in the case of the 
transit of 1874 ; not one of the above places differing by much more than 
300 miles from the corresponding place ” obtained by the Astronomer 
RoyaL 
The Aurora , the Zodiacal Light, and the Sun's Corona. — A series of very 
remarkable observations by Angstrom, the Swedish astronomer, and by 
Professor Young during the recent total solar eclipse in America, seem to 
associate the aurora, the zodiacal light, and the sun’s corona in a very sin- 
gular manner. All three appear to give the same spectrum, with this 
difference, however, that the lines are not equally strong. Strangely enough 
one of the lines seen in the spectra of these lights belongs to iron. The fact 
that the zodiacal light and the solar corona should give bright lines at all is 
sufficiently remarkable, since a spectrum of bright lines is usually indicative 
of gaseity. However, there seems no reason to doubt the exactness of the 
observations, though some of the American astronomers speak of the spec- 
trum of the corona as continuous. It is obvious that there is nothing in the 
fact that the coronal spectrum consists principally of bright lines, incon- 
sistent with the fact that a portion of its light should give a continuous 
spectrum. 
