42 NATURE 
[MarcH 14, 1912 
communication is by Prof. Onnes, and deals with the 
electrical resistance of mercury at these low tempera- 
tures. The resistivity of mercury in the solid state 
at the melting point is about 50 ohms per centimetre 
cube. As the temperature decreases it falls regu- 
larly to 0°12 ohm at 43° absolute. In the interval 
between 423° and 418° absolute it falls to a value of 
the order 10o-° ohms per centimetre cube, that is, it 
practically disappears. 
Two of the late Prof. Van’t Hoff’s former students, 
Dr. W. P. Jorissen, of Levden, and Dr. L. Th. 
Reicher, of Amsterdam, have recently published a 
very interesting volume entitled ‘“‘ J. H. Van’t Hoff’s 
Amsterdamer Periode, 1877-1895’ (Helder: C. de 
Boer, jun., 1912, pp. 106). Dealing principally with 
Van’t Hoff’s work as a university professor in 
Amsterdam, the book contains also an account of the 
teaching of chemistry in Amsterdam before Van’t 
Hoff’s arrival, a short account of his life, and a 
detailed bibliography of his published books and 
papers, and of the biographical and other notices 
which have been written concerning the great Dutch 
chemist. The illustrations form a very interesting 
feature of the volume, consisting of portraits of Van’t 
Hoff at different periods of his life, portraits of his 
predecessors at Amsterdam, and pictures of the 
Amsterdam Chemical Laboratory in the various 
stages of its history. The book forms an important 
contribution to the history of Van’t Hoff’s life and 
work, and the authors are to be warmly congratu- 
lated, not only on the affectionate piety which has 
inspired their work, but also on the care and labour 
that they have bestowed upon it. 
Engineering for March 8 gives some additional 
particulars of the oil-engined ship Selandia, the first 
passenger sea-going vessel fitted with Diesel engines. 
There are two main engines, driving twin screws, 
each engine consisting of a set of eight single-acting 
cylinders 202 in. in diameter by 28°75 in. stroke, work- 
ing on the four-stroke cycle. It is evident from the 
successful running that no pains and no expense have 
been spared in rendering the auxiliary machinery as 
immune from breakdown as is possible. During the 
voyage from London to Antwerp, the indicated-horse- 
power developed in eight cylinders was 1190, or 1000 
brake-horse-power, assuming 84 per cent. efficiency 
as obtained on the test bed at the maker’s works. 
The fuel-oil consumption is about 0°45 Ib. per brake- 
horse-power hour. The indicator diagram shows a 
mean pressure of about 91 lb. per square inch at 
129 revolutions per minute. It is claimed that this 
type of engine has increased the cargo-carrying 
capacity by 1000 tons. 
In the article upon ‘Soot’? which appeared in 
NaturE of February 29, reference was made to an 
article upon ‘‘The Sootfall of London” which 
appeared in The Lancet of January 6. Mr. S. Archi- 
bald Vasey writes to point out that the experimental 
portion of the inquiry was done entirely in The Lancet 
laboratory under his personal supervision. Messrs. 
des Vceux and Owens took no part in the laboratory 
work, which included some 400 analyses, though their 
names were associated with it in our article. 
NO. 2211, VOL. 89] 
OUR ASTRONOMICAL COLUMN. 
Discovery or a Nova.—A telegram received from 
Kiel yesterday states that a new star, of the fourth 
magnitude, has been discovered in the neighbourhood 
of » Geminorum by Herr Enebo, of Domaas, Norway. 
7» Geminorum transits about 6.30 p.m., and sets near 
the north-west at about 2 a.m. 
EPHEMERIDES OF ComeEts.—A continuation of the 
ephemeris of Brooks’s comet (1911c) is published by 
Prof. Millosevich in No. 4558 of the Astronomische 
Nachrichten, and shows that the comet is in the 
southern extremity of Circinus, and is very faint. 
Schaumasse’s comet (i1911h), according to the 
ephemeris published by the discoverer in the same 
journal, is almost stationary about half-way between 
B and ¢ Ophiuchi, and is about eight times less 
bright than when discovered. An observation on 
February 16 showed the comet to be excessively 
feeble. 
In No. 4559 of the journal Dr. Ebell publishes new 
elements for Quénisset’s comet (1g911f), and gives an 
ephemeris covering the period April 5 to May 15. 
The comet is now in Carina, and is of about the 
tenth magnitude. 
OBSERVATIONS OF BIELIDS IN NOVEMBER, IQII.— 
Assisted by four students, Prof. Pokrowski kept 
watch for the Bielid shower of meteors on November 
17 and the succeeding nights. On the first night 
twenty-six meteors were seen between 8h. and 12h. 
(Dorpat M.T.), and of twelve seen between 8h. and 
toh. nine appeared to come from a radiant at 24°, 
+42°. Four meteors from 25°, +42° were seen on 
November 24, and on several nights other radiants 
given in Denning’s catalogue were seen to be active. 
THE SMITHSONIAN ASTROPHYSICAL OBSERVATORY.— 
Mr. Abbot’s report for the year ended June 30, I1o1T, 
contains some most interesting results, chiefly con- 
cerning the sun’s radiation. 
He emphasises the fact that simultaneous observa- 
tions have now been made at Washington (sea-level), 
Mount Wilson (altitude, more than a mile), and 
Mount Whitney (altitude, nearly three miles), and 
that the close agreement of the results indicates that 
the effects of the earth’s atmospheric absorption are 
practically eliminated. From the observations made 
during 1902-10, the general mean for the solar con- 
stant is found to be 1922 calories (15° C.) per sq. cm. 
per minute. The solar radiation appears relatively 
greater in the infra-red than in the ultra-violet, 
possibly because the shorter radiation from the deeper 
layers of the solar atmosphere are selectively absorbed 
during their passage through the upper layers; but, 
taking all things into consideration, it is probable 
that we receive solar radiations from sources having 
temperatures between 5000° and 7o00° abs. C., and 
mostly between 6000° and 7oo0°. The observations 
tend to confirm the existence of an irregular varia- 
tion in the solar radiation from day to day; its ampli- 
tude is from 3 per cent. to 10 per cent., and its period 
ranges between five and ten days. 
Observations from the summit of Mount Whitney 
show that one square degree of polar sky, at night, 
gives 0'0746 the light given by a first-magnitude star, 
and that the observed increased brightness of the 
night sky near the horizon must be ascribed to some 
terrestrial agent, such as a continuous faint aurora. 
OBSERVATIONS OF SUN-SPOTS AND FACUL2 IN IQII. 
—Prof. Ricco’s annual summary of the solar observa- 
tions made at Catania during 1911 appears in No. 1, 
vol. i. (second series), of the Memorie della Societa 
