1872.] Microscopy. 269 
An interesting observation upon the influence which the temperature of the 
prism exercises upon the position of the lines has been made by M. Blaserna. 
It has already been noticed by Verdet, that where liquids are used for prisms, 
the displacement of the lines is quite noticeable, the index of refraction 
altering with the temperature. For solid prisms, however, it was assumed 
that the influence of change of temperature upon their refractive power was 
quite insignificant. M. Blaserna has found, however, upon observation, that 
this is not so unimportant as is generally believed ; but that, while much less 
sensitive than liquid prisms, the displacement of lines could readily be 
observed with one of flint glass. The prism used in the experiment was one 
of Duboscq’s, and was exposed for some time to the dire& rays of the sun. It 
was then quickly placed in a spectroscope in the shade and some prominent 
line observed, when it was found that as the glass cooled the refractive power 
increased. (An opposite result is obtained for bisulphide of carbon). He was 
able to observe in this manner a displacement of the p line, amounting to 3" 
for a difference of temperature equal to 1° C. In the instrument used 
the interval between pD and Dp’ is 12”, so that a change of 4° C. would 
suffice to place D in the position of p’. M. Blaserna remarks, as the result of 
his interesting observation, that an error might very readily be made in spec- 
troscopic work, by comparing together observations made in sunlight and 
in shade, or those made in the morning with those in the night. 
In “ Poggendorff’s Annalen,” M. L. Schonn contributes a paper on the employ- 
ment of cylindrical lenses in spectroscopic observations. As in observations of 
the spectrum we have to do with lines of light, and these, moreover, straight 
ones; and as, in addition, it is not necessary that the rays falling on the 
prisms should all be parallel to each other, but only that they should all be in 
parallel planes, M. Schonn thinks it would be far better to make use of 
lenses suited to this especial purpose, and to employ throughout none but 
cylindrical lenses also for illuminating the slit. From a preliminary examina- 
tion he has ascertained that one thus obtains well-defined spedtra, in which 
the full extent of the prism is rendered available. Perhaps, also, another dis- 
position of the spectrum might at the same time be recommended—namely, 
one wherein the image of the slit should be horizontal, inasmuch as lines that 
lie in a horizontal position are seen with greater precision. 
Just before going to press we received, through the Royal Astronomical 
Society, an announcement of the discovery of a minor planet (118), Peitho, at 
Bilk, by Dr. R. Luther. 
M.T. at Bilk. 
, ” 
1872. 5 ail RE h,; m. Js: a 
March 15 14 18 59°6 [Revi Ss 1G] AAS PaIR INoleHID), = Fe) 1 BI) 
From an observation made by Dr. Tietjen, at Berlin :— 
M.T. at Berlin. 
1872. hs ms: Dies. 
March 21 g 33 23 Resor if a1oPs(6) NSE: Ds — 79) 201 4675 
The daily motion obtained from these observations is in R.A. — 60°6", and in 
N.P.D.—3' 45". The planet is of the 11th magnitude. 
fo} , ” 
Microscopy.—An improved erector for use with binocular microscopes has 
been contrived by R. H. Ward, M.A., M.D., Professor of Botany and Micros- 
copy in Rensselaer Polytechnic Institute, U.S. The lenses of a 1} or 2-inch 
objective may be packed or screwed into the upper end of an adapter, which 
when screwed into the nose-piece of the microscope, carries them up close to 
the binocular prism, and into the lower end of which the obje&-glass may be 
screwed. A more convenient arrangement is an adapter with a sliding tube 
adjustment, which varies to the extent of an inch or more the distance 
between the erector and objective. Different powers and distances will of 
course be used according to the wants of different observers. The combina- 
tion considered most convenient by the inventor consists of a 2-inch erecting 
lens close to the binocular prism, and a 3-inch objective at a distance mea-- 
sured to its lower end of from 3 to 44 inches below the erector, giving powers 
