June 13, 1907] 



NATURE 



161 



ij°, 30", 45°, and its interest would appear to lie, not 

 so much in the use of groups for teaching trigonometry, 

 but rather in the possibilities of using trigonometry for 

 illustrating the elementary stfidy of groups. 



In a paper on the chemical actions of light, M. P. 

 V'illard describes in the Journal de Physique (vi., May) 

 certain continuation phenomena. An interesting experi- 

 ment is illustrated showing the effect of green light on 

 photographic papers containing tartaric acid. A sheet 

 o( such paper was under-e.vposed under a stereoscopic 

 negative ; one part was then submitted to green and 

 another to violet light. On the green part an excellent 

 image developed, while the violet rays completely fogged 

 the other part. The use of green glass in intensifying 

 prints thus finds a ready explanation. 



In the Journal of the .Asiatic Society of Bengal (1907, 

 vol. iii.. No. 2) Prof. P. C. Ray describes the preparation 

 of a silver mercuroso-mercuric nitrate by the action of a 

 solution of mercurous nitrite on silver nitrite. The com- 

 pound formed has the composition Hg"(Hg',Ag)j(N03),, 

 and is of interest as showing that univalent mercury has 

 the power isomorphously to replace silver. In an article 

 on the " Pursuit of Chemistry in Ancient India," pub- 

 lished in the Modern Review of Allahabad, Prof. RSy 

 shows, by reference to old Sanskrit writings, the antiquity 

 of the knowledge of chemistry in this country, particularly 

 as regards metallurgical processes and the preparation of 

 medicaments. The existence of an enormous wrought- 

 iron pillar at Katub, near Delhi, which dates back to 

 about A.D. 400, and is larger than any forged in Europe 

 until quite recently, is a striking illustration of the high 

 state of development of the arts in ancient India prior 

 to their decay caused by the introduction of a new caste 

 system under the later religious teachers. 



The uncertainty which still exists regarding the latent 

 heat of fusion of ice forms the subject of a paper by 

 Mr. L. F. Guttmann in No. 4 of the Journal of Physical 

 Chemistry. The values obtained by Regnault (79-2) and 

 by Bunsen (8o-o) for this fundamental constant differ by 

 more than i per cent., and it is contended that Bunsen 's 

 result is vitiated by the fact that the value obtained for 

 the density of solid ice at 0° is very variable and un- 

 certain, depending, apparently, on the age of the ice. The 

 value 7559, re-calculated from Regnault's determinations 

 by introducing certain corrections for the specific heat of 

 ice and water, is considered to represent most accurately 

 the true value for the latent heat of fusion of ice. It would 

 appear, however, that Mr. Guttmann, while referring to 

 the recent work of M. Leduc on the same subject pub- 

 lished in the Comptes rendus (1906, vol. cxlii., p. 46), has 

 overlooked the more detailed account given by the same 

 author of his investigations in the Journal de Physique 

 (see Nature, vol. l.xxiv., p. 41). The difficulties raised by 

 Mr. Guttmann were there dealt with, and, after introducing 

 all necessary corrections, a value of 79-2 was deduced for 

 the latent heat as being in harmony, not only with 

 Regnault's determinations, but also with the corrected 

 values calculated from Bunsen 's data. 



Messrs. C. E. Muller, Orme and Co. have sent us 

 their flow extraction cup apparatus. This apparatus is an 

 improved form of the Soxhlet extractor. Two forms of 

 cup are used ; in one case the cup has a siphon, so that 

 the substance which is being extracted is kept covered 

 by the solvent, and a continuous flow of the pure hot 

 solvent is kept running directly through the substance. 

 The otTier cup, which has a perforated bottom, is placed 

 NO. 1963, VOL. 76] 



in an outer cup, which is so arranged that the inner cup 

 stands about i cm. above it. By this means the cup is 

 kept continuously surrounded by the hot solvent. We have 

 tested this apparatus, and find the extraction to be both 

 rapid and efiicient. The cups are of glass, and are there- 

 fore very convenient for weighing the substance both before 

 and after extraction. There is also an arrangement for 

 distilling off the solvent after the extraction is completed. 



The 1907 issue of " The Statesman's Year-book " pro- 

 vides, in the convenient form one has learnt to expect in 

 this invaluable anuual, the latest available statistics con- 

 cerning the States of the world. In some cases the in- 

 formation comes up to within a few weeks of publication. 

 One pf the most important of the new fe;itures of the 

 volume is the section, which has been entirely re-written,- 

 relating to the armies of the various States. Diagrams 

 and tables are included exhibiting the comparative growth 

 of the leading navies in the past with a forecast of the 

 future. Maps are also given showing the Anglo-French 

 Nigerian boundary, the Turko-Egyptian boundary (1906), 

 the new boundary of .Aden protectorate, and the increase 

 in value of land and property in Great Britain. This is 

 the forty-fourth publication of the annual, and Dr. J. Scott 

 Keltic, its editor, is to be congratulated on maintaining 

 its high standard of accuracy and usefulness. 



A BIOGRAPHICAL sketch of the life and writings of 

 Linnaeus, by D. H. Harms, appeared in the Naturwissen- 

 schaftliche Wochenschrift of May 19. 



OUR ASTRONOMICAL COLUMN. 



Co.met iqo7c (GiAcoBiNi). — Circular No. 97 (June 6) from 

 the Kiel Centralstelle gives a set of elements and an 

 cphemeris for the faint comet discovered by M. Giacobini 

 on June i. From the ephemeris it is seen that the comet 

 is travelling eastwards through Leo, and will pass about 

 I5 degrees north of 5 Leonis on June 14; its brightness is 

 decreasing slowly. 



Mars. — In Bulletin No. 26 of the Lowell Observatory 

 Prof. Lowell gives the results of the observations of the 

 south polar cap of Mars made during the favourable 

 presentation of 1905. 



Owing to the adverse tip of the planet's axis and the 

 distance of Mars from the earth at the suitable season of 

 the Martian year, the mapping of the southern cap has 

 not previously been attempted. The present communica- 

 tion gives the latitudes of the edge of the snow in suc- 

 cessive longitudes as determined from some two hundred 

 drawings. The extent of the snow cap as seen during the 

 presentations from May 10 to -August 14 is shown on three 

 diagrams. 



The observations indicate that during the beginning of 

 the opposition cloud or mist enveloped the cap, for not 

 until May 15 was the edge of the cap continuously recog- 

 nised, although snow was seen, in latitude 3i°-8 S., on 

 January 25. 



In a telegram, published in Circular No. 97 from the 

 Kiel Centralstelle, Prof. Lowell announces that Mr. Lamp- 

 land has photographed the Martian canals Thoth and 

 Astaboras. 



.\ Third .Asteroid near Jl'piter's Orbit. — From a deter- 

 mination of the orbital elements of the minor planet 

 iqo6 VV, Herrn Vladimir Heinrich finds that in this 

 object we have a third member of the Jupiter group of 

 asteroids. According to the elements yet determined, the 

 length of the semi-major axis of the orbit is about 5- 19 

 astronomical units (Astronomische Nachrichten, No. 4181, 

 p. 88, June i). 



Radial Velocities of e and C Cvgni. — Observations 

 made at Bonn during 1904-5-6 indicate that the period 

 of the r.adial velocity of € Cygni is possibly shorter than 

 that exhibited by the Lick observations of this star. Prof. 

 Kiistner finds a variation, of the radial velocity in regard 



