January 21, 1897] 
smooth surface of the metal; and the coefficients of expansion 
of the two constituents are for all practical purposes identical. 
The economy of the system in the construction of girders and 
arches is considerable, owing to the great strength and compact- 
ness obtained, and. further, the material is absolutely fire-proof. 
Large spans may be used for floors, and the small amount of 
head-room required is a factor often of great value. The system 
can also be used in situations where brick and stone would be 
impossible. 
Ir is well known that air-currents containing either drops of 
water or fine dust in suspension give rise to electrification when- 
ever they impinge on a solid obstacle. M. P. de Heen, guided 
by the view that electricity, independently of all luminous phe- 
nomena, can produce photographic impressions, has tried the 
experiment of allowing a current of air, laden with Lycopodium 
powder, to fall on a sensitive plate, and the photograph thus 
obtained is reproduced in the Azd/eézn of the Belgian Academy. 
With an uncovered plate, a feeble but distinct impression was 
obtained after one and a half hours, but by using a covered 
plate a much more powerful impression was produced. The 
most remarkable feature is that where the covering has been 
broken away dark ramifications are seen extending some dis- 
tance into the covered portion, and these appear to follow the 
directions in which electricity has been propagated along the 
surface of the plate. In this connection attention may well be 
directed to the experiments described on p. 269 of this number 
of NATURE. 
THE relative transparency of the alkaline metals to Rontgen 
rays, forms the subject of a note by Prof. C. Marangoni in the 
December number of the A¢é2 det Lincez. The author draws 
the following conclusions: (1) The most transparent metal is 
lithium, and its transparency does not increase with the thick- 
relative to potassium would suggest that the transparency for 
these rays is a function of the atomic weight as well as of the | 
density. 
Ir is satisfactory to note that local fishery authorities are 
becoming increasingly interested in the scientific study of sea 
fisheries. The Northumberland Sea Fisheries Committee 
carried out in the summer of 1896 a series of trawling excursions 
in the bays of its district for the purpose of examining their 
condition and their productiveness, and a report on the results, 
drawn up by Mr. Alex. Meek, has been published. Mr. Meek 
is attached to the Durham College of Science at Newcastle-on- 
Tyne, and the more deliberate studies of the material collected 
were carried on in that institution. The report contains 
interesting details concerning the animals captured in trawl and 
tow-net, the pelagic eggs, and the food of the fishes. 
THE latest instalment of the ‘‘ Account of the Crustacea of 
Norway with short descriptions and figures ofall the species,” 
which Prof. G. O, Sars is publishing, forms the commencement 
of vol. ii., and of the description of the Isopoda. The general 
remarks on the Order only occupy three pages. The classifica- 
tion employed is that adopted by the author in 1882, the Order 
being divided into six tribes according to the characters of the 
first pair of legs, of the last pair of appendages (uropoda), and 
of the five pairs in front of the last (pleopoda). The first 
tribe, Chelifera, is distinguished by the fact that in its 
members the legs of the first pair are cheliform, that is, have 
prehensile claws. Twenty-six species in this tribe are de- 
scribed, and these are figured on sixteen autograph plates. 
In the last number of the Records of the Geological Survey 
of India, there is recorded a discovery by Dr. J. W. Evans, 
which adds another to the long list of geological resemblances 
between the peninsula and South Africa, and is also of some 
NO. 1421, VOL. 55 | 
NATURE 
ness ; (2) the anomaly of the greater transparency of sodium | valuable *work,jandsdesls wath the /Etypndcez: 
279 
economic importance. This is the sedimentary nature of the 
gold-bearing rocks of Mysore, Dr. Evans having proved that 
what had been regarded as a quartz vein is in reality a 
quartzite. 
THE following are among the lectures to be delivered at the 
Royal Victoria Hall, Waterloo Road, during February :— 
February 2, Mr. H. Bernard, on ‘‘ Scorpions and their Rela- 
tions”; February 9, Mr. R. A. Gregory, on ‘ Photography of 
the Heavens”’; February 23, Dr. J. W. Waghorn, ‘‘X and 
other Rays of Light.” 
THE fiftieth annual general meeting ot the Institution of 
Mechanical Engineers will be held on Thursday and Friday, 
February 4 and 5. On each occasion the chair will be take 
by the President, Mr. E. Windsor Richards. 
“Fourth Report to the Alloys Research Committee,” by Prof, 
W. C. Roberts-Austen, C.B., F.R.S. (Thursday) ; ‘‘ Partially 
Immersed Screw-Propellers for Canal Boats ; and the influence 
of Section of Waterway,” by Mr. Henry Barcroft (Friday) ; 
“* Mechanical Propulsion on Canals,” by Mr. Leslie S. Robinson, 
of London (Friday). 
THE first number for the current year of the Bzologisches 
Centralb/att contains the commencement of an important article, 
by Dr. T. Bokorny, on the organic nutrition of green plants, 
and its importance in nature. 
NuMBER I of vol. xxxii. of the Proceedings of the American 
Academy of Arts and Sciences is devoted to contributions from 
the Gray Herbarium of Ilarvard University, of interest to students 
of the flora of the United States. 
Part xvil. of Dr. R. Braithwaite’s ‘‘ British Moss-Flora” 
has just been received. It commences Section 8 of this very 
The two re- 
maining families of Pleurocarpous mosses will be described in 
future parts. . 
We have received the Part for December 1896 of the Agricul- 
tural Students’ Gazette, edited by students at the Royal Agricul- 
tural College, Cirencester. It contains papers on coffee-planting 
in British Central Africa ; on clearing and preparing forest-land 
for cane in Queensland ; and on experiments on permanent grass 
on the Lydney Park Estate, Gloucestershire. 
Mr. STEPHEN MARRIOTT has sent us a little book of his, 
entitled ‘‘To Winnipeg, Manitoba, and Back” (Simpkin, 
Marshall, and Co.). Though primarily of interest to intending 
emigrants, it contains much information worth reading ; and, in 
view of the visit of the British Association to Canada this year, 
should find readers in the scientific world. 
THE additions to the Zoological Society’s Gardens during the 
past week include two-Patas Monkeys (Cercopithecus patas, 5 2) 
from West Africa, presented by Mr. W. Loy ; a Prairie Marmot 
(Cynomys ludovicianus) from North America, presented by Mr. 
W. Hewlett ; two Kestrels (7zznculus alaudarius), British, 
presented by Miss Fanny D’Aeth; a Greater Black-backed 
Gull (Zarus marznus), British, presented by Mr. W. Theobald ; 
a Pardine Lizard (Acanthodactylus pardus), a Scutellated Lizard 
(Acanthodactylus scutellatus) feom Biskra, Algeria, presented by 
Mr. H. B. Hewetson; two Indian Pythons (Python molurus) 
from India, three West African Pythons (Python sebe), 
deposited. 
OUR ASTRONOMICAL COLUMN. 
Comet PERRINE 1896, DECEMBER 8.—In this column for 
December 31, 1896, we referred to the striking similarity 
between the elements of the comet discovered by Mr. Perrine 
on December 8, and those of the Biela comet. Dr. F. Risten- 
part finds, however (str. Nachr., No. 3396), that the resem- 
