250 
NATURE 
[May 9, 1912 
dawn and later, the effect of mist or an approach- 
ing storm on the distribution, and, lastly, the means 
talken in artificial illumination to imitate daylight. 
In the February number of the Bulletin of the 
Academy of Sciences of Cracow, Prof. Natanson has 
an article on the energy content of material bodies 
in which he points out an important distinction between 
Prof. Planck’s theory of radiation and Prof. Einstein’s 
idea that every material body consists of an 
assemblage of Planckian vibrators, the energy of 
which constitutes the heat energy of the body. While 
in the general theory of radiation it is unnecessary 
to inquire how many vibrators of a given period are 
present per gram of a material, so long as the inter- 
change of energy of different wave-lengths can be 
effected by their means, in the latter theory it is of 
fundamental importance to determine the number of 
each kind present. Without this knowledge Prof. Ein- 
stein’s interesting theory cannot be pursued further. 
In the course of a valuable paper on ‘‘Some Aspects 
of Diesel Engine Design,” read by Mr. D. M. 
Shannon at the Institution of Engineers and Ship- 
builders in Scotland, the author takes up the im- 
portant question of the proper design of cams for 
operating the valves. The noise caused by some cam 
and roller gears is due principally to two causes, the 
first and greater being the speed with which the cam 
strikes the roller, and the second being the valve 
striking the seat. The latter need cause no incon- 
venience, since it occurs inside the cylinder, and is 
therefore of a muffled nature. To get rid of the 
former cause, the flat part of the cam profile should 
slide under the roller at a tangent, and should grip 
the roller with no velocity. If this is done, the valve 
can then be pushed open as rapidly as desired. The 
closing of the valve should be obtained in a similar 
manner. Diagrams are given showing the abrupt 
changes in speed and acceleration produced by a badly 
designed cam, and are contrasted with the curves given 
by a cam properly designed. There are many makers 
of internal-combustion engines who might profit by a 
careful study of Mr. Shannon’s paper. 
Messrs. J. anp A. CHURCHILL have just ready for 
publication vol. vi. of the new edition of ‘‘Allen’s 
Commercial Organic Analysis.” This volume has 
been rewritten under the editorship of Mr. W. A. 
Davis and Mr. S. S. Sadtler. 
Amonc the new books and new editions announced 
for publication by Messrs. C. Griffin and Co., Ltd., 
are the following :—‘‘ Practical Agricultural Bac- 
teriology,” Prof. Lohnis, translated by W. Stevenson ; 
‘Notes on Foundry Practice,” J. J. Morgan; ‘‘ Modern 
Road Construction,” F. Wood; “Modern Pumping 
and Hydraulic Machinery,” E. Butler; ‘‘ Calculations 
on the Entropy Chart,” Dr. W. J. Crawford; ‘ The 
Evolution of the Internal Combustion Engine,” E. 
Butler; ‘‘The Gas Turbine, Theory, Construction, 
and Working Results of Two Machines in Actual 
Use,” H. Holzwarth, translated by A. P. Chalkley; 
‘“A Manual of Marine Engineering: comprising the 
Designing, Construction, and Working of Marine 
Machinery,” A. E. Seaton; ‘‘A Treatise on Mine Sur- 
veying,”” H. Brough, revised by Prof. S. W. Price; 
NO. 2219, VOL. 89] 
I. Electrical Photometry,” Prof. H. Bohle; ‘* Celluloid,” 
a translation from the French of Masselon, Roberts, 
and Cillard, by Dr. H. H. Hodgson; ‘‘ A Handbook on 
Metallic Alloys,” G. H. Gulliver; ‘‘ Mathematics and 
Mechanics for Technical Examinations,’ C. A. A. 
Capito. 
OUR ASTRONOMICAL COLUMN. 
A Brituianr Mereor.—A meteor of unusual bril- 
liance and low velocity was observed by Mr. Rolston 
at South Kensington at gh. 46m. (G.M.T.) on May 2. 
The approximate commencement and end of the flight 
were at 150°+14°, and 1423°, o°, respectively, and 
the time occupied in traversing the path was esti- 
mated as at least two seconds. Both in colour and 
brightness the meteor was very like Arcturus, and no 
train was visible along which it had passed. The 
position of the commencement of the apparition is a 
little uncertain, because Mr. Rolston was not actually 
engaged in watching for meteors, his attention being 
first directed to the phenomenon by its extraordinary 
brightness. 
Nova GeminoruM, No. 2.—In No. 4569 of the 
Astronomische Nachrichten, Prof. Max Wolf publishes 
some remarks on the apparently periodical changes in 
the structure of the complicated hydrogen bands in 
the spectrum of Nova Geminorum. As Prof. Iniguez 
has pointed out, the most intense portion of each band 
has changed its position in the band, and Prof. Wolf 
finds that a certain periodicity is displayed by the 
variations. The brightest part moves gradually, first 
towards the red and then towards the violet, the 
changes taking place in regular steps in about four- 
teen, or seven, days. Thus on March 15 and 29 the 
dark absorption line in the Hd band, at A4093, became 
obvious, and on April 13 the structure of the band 
was similar to that which obtained on March 17. 
It is suggested that the seven-day magnitude varia- 
tion remarked by Dr. Kritzinger may be related to 
these changes in the structure of the spectral bands. 
Fant Stars witH Larce Proper Morions.—The 
comparison of photographs of several star clusters 
taken in 1909-10 with the large Pulkowa astrograph 
with similar plates taken eleven to fifteen years 
earlier has disclosed a number of large proper motions, 
of which Herr Kostinsky gives particulars in No. 4569 
of the Astronomische Nachrichten. The magnitude 
of the proper motions was measured in the first place 
with a Zeiss stereocomparator, and was shown in 
every case to be more than 1o” per century on a great 
circle. The annual motions of the seven stars de- 
scribed range from 0113” to 111” on a great circle. 
Four pairs of plates, having intervals of about one 
year, show that the star BD+53° 2911 (mag. 9°5) has 
a mean annual proper motion of 1'23”+0'04"; this star 
appears on the photographs of the Nova Lacertz 
(1910) region, its position (1911’0) being 22h. 29m. 
TO¢2Sey 153° 20) 3)": 
SoraR PROMINENCES IN IgI0.—Prof. Riccd pub- 
lishes his annual (1910) summary of the prominences 
observed at Catania in No. 3, vol. i., series 2, of 
the Memorie della Societa degli Spettroscopisti 
Italiani. It shows that while from month to month 
the mean frequency of prominences varied irregularly, 
there was, on the whole, a regular decrease in the 
northern hemisphere, while the frequency was fairly 
constant in the southern. For the four trimestres 
the frequencies were :—N. hemisphere, 2-3, 1-5, II, 
and o-4; S. hemisphere, 1-4, 13, 13, and 1-3, re- 
spectively, the mean frequencies for the year being 
1-3 in each hemisphere. This gives 2:6 as the mean 
frequency for both hemispheres, a value notably 
smaller than that for the immediately preceding 
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