238 



NATURE 



\yan. 20, 1876 



each series of observations ; and in" the original paper lull 

 details of the observations are given, together with tables, show- 

 ing the agreement between the calculated and observed results, 

 and also*^ (after tlie necessary corrections and reductions have 

 been made) between the volumes calculated from the formulae 

 from different series of observations in the same solutions. 

 Finally, a general formula of the form 



was found, giving the relation between the volume (z/), tempe- 

 rature (/), and specific gravity at o" C. (j) of any solution of the 

 same composition of sea-water the specific gravity of which at 

 o" C. lies between i '020 and i -033, the volume at the same 

 temperature being taken as unity ; in which expression 



d)(/) = I + -00008097/ + -0000049036^^ - -OOOOOOOI2289f'*, 



^{f) = - 10-' (-5509;'- -020198/2 _. 00033276^ 3^, 

 and 



f{s) = 11-95 - 94o(.f - I '02). 



In the original paper it is shown that if a be the specihc 

 gravity at any temperature t and of a solution the specific gravity 



of which at 0° C. is J,' — may without sensible error be as- 



d s 

 sumed to be constant ; whence, by means of the above formula, 

 the authors are able to give in a table all the data necessary for 

 calculating the specific gravity of sea-water ^of any degree of 

 salinity at any temperature between 0° and 36°. 



The authors conclude by discussing the discrepancies which 

 occur between their results and those of Prof. Hubbard ; and 

 they point out various circumstances in the methods employed in 

 making and reducing the latter observations which appear to 

 them to explain in a great measure the divergences which 



On the Action of Light on Tellurium and Selenium. By Prof. 

 W. G. Adams, F.R.S. 



A small bar of tellurium, an inch long, whose resistance was 

 half an ohm, formmg part of one of the resistances in a Wheat- 

 stone's Bridge, was exposed to the light of a paraffin lamp at a 

 distance of half a metre from it. At first, on exposure, the heat 

 from the lamp increased the resistance of the tellurium. 



When a rectangular vessel of water was placed between the 

 lamp and the tellurium there was found, on exposing as before, 

 to be no perceptible change in the resistance. On removing the 

 rectangular vessel and putting a cyUndrical beaker of water in its 

 place, so as to focus the light on the tellurium, the resistance of 

 the tellurium was found to be diminished. 



When it had been kept in the dark for several days the tel- 

 lurium was much more sensitive to light. When exposed to the 

 paraffin lamp the resistance of the tellurium was now found to be 

 as much diminuhed without using the beaker of water as it had 

 previously been when the beaker was used, On introducing the 

 beaker of water between the tellurium and the lamp, the resist- 

 ance of the tellurium was still further diminished, the change 

 produced in the resistance by the exposure being ^th part of 



the whole. , , , 1 ^ ^i. 



When the selenium bar was exposed to the same lamp at the 

 distance of I metre, the change in the resistance was ^th of the 



■whole. , , r T ui. .. 



On exposing the selenium to a constant source of light at 

 different distances, the change in the resistance of the selenium 

 is inversely as the distance, i.e., directly as the square root of the 

 illuminating power. , . , . , ji j 



The following results were obtained with one candle and an 

 argand lamp, whose illuminating power is equal to sixteen 



At i metre. At i metre. At i metre. At 2 metres. 

 With argand lamp — ... 17° ••• 83 ... 39 

 With I candle ... — ■•• 4i •-• ^% -•- % 

 With I candle ... 82 ... 39 ••• i» --• * 



These and other similar experiments clearly show that the 

 change in the resistance of the selenium is directly as the square 

 root of the illuminating power. 



Mathematical] Society, Jan. 13.— Lord Rayleigh, F.R.S. , 

 vice-president, in the chair.— Major J. R. CampbeU, Mr. R. P. 

 ScotC and Prof. H. W. Lloyd Tanner were admitted into the 

 Society. —The following communications were made :— Mr. 

 T W L. Glaisher, F.R.S., on an elliptic-function identity.— 

 Prof H. W. Lloyd Tanner on the solution of partial differential 

 equatioiis of the second order with any number of variables 

 when there is a complete first integral.— Prof. Clifford, F.K.b., 

 on free motion of a rigid system in ah «-fold homoloid j 



expression of the velocities by Abelian functions. — The fol- 

 lowing abstract of Prof. Clifford's paper will give some idea 

 of the mode of treatment employed : — Equations correspond- 

 ing to Enler's are obtained for the 4«(« - l) rotations /,,k ; 

 these are A|,,.</t/|,k = 2/1,1/^1 where the \ are expressed in 

 terms of the n constants a, namely, Ahk(*ii ~ "k) = *h + *k 5 ^* 

 is understood that /,,^ = - /,j,,. It is then shown that similar 

 equations are satisfied by quotients of 6-functions of « - 2 argu- 

 raents, one argument being at + e. The solution of the problem 

 for the rotational velocities in n variables carries with it the 

 determination of the position in the case of « — I variables ; the 

 co-ordinates of the principal points are thus expressed in terms 

 of the combinations of t^-functions which Rosenhain used for the 

 inversion of integrals of the third class. — Lord Rayleigh, F.R.S., 

 on the approximate solution of certain potential problems. 



Royal Astronomical Society, Jan. 14. — Prof. Adams, 

 president, in the chair. — A paper by the Astronomer Royal was 

 read on the present state of his calculations for his new lunar 

 theory. — Capt. Orde Browne read a paper on the times of the 

 phenomena of the Transit of Venus. He compared the times 

 given by the observers at the different Egyptian stations, and 

 showed that the observations might be divided into three classes, 

 in the first of which it seemed probable that the observers had 

 noted as the time of internal contact the moment at which a 

 shadoivy ligament was first formed between the limbs Of the 

 planet and the sun. In the second class it appeared that the 

 observers had noted as the time of internal contact the moment 

 at which a black ligament, as dark or nearly as dark as the 

 planet's disc, was first seen between the limbs of the planet and 

 the sun; observers of the third class had waited for what he 

 termed geometrical contact, or the moment when the discs 

 of the planet and the sun appeared to have a common 

 tangent. Mr. Burton said that the chief difficulty which he had 

 experienced in noting the exact moment of internal contact at 

 ingress arose from the bright line which was seen surrounding 

 the dark limb of the planet before it entered upon the sun's 

 disc, this prevented him from determining the moment when 

 the solar cusps actually met around the disc of the planet. — 

 Mr. Christie described a new form of solar eye-piece which he 

 had devised. It consisted of a series of glass prisms placed 

 between the eye-piece and the eye of the observer in such a 

 manner that the light was reflected nearly at the polarising 

 angle, and when the prisms were turned round relatively to one 

 another, the intensity of the ray entering the eye could be ad- 

 justed with great nicety. The chief advantages of this plan 

 were that by placing the prisms between the eye-piece and the 

 eye the reflecting surfaces could be kept small and the eye-piece 

 could be used as a photometer for comparing the intensity of 

 very bright lights, as it was evident that the intensity of the re- 

 flected and emergent rays could be easily calculated directly the 

 positions of the prisms were known. 



Geological Society, Jan. 5.- Mr. John Evans, F.R.S., 

 president, in the chair.— John Kenworthy Blakey, Frederick 

 Hovenden, and Thomas Lovell, M. Inst. C.E,, were elected 

 Fellows of the Society.— The following communications were 

 read :— Historical and personal evidences of subsidence beneath 

 the sea, mainly if not entirely in the fourteenth and fifteenth 

 centuries, of several tracts of land which formerly constituted 

 parts of the Isle of Jersey, by Mr. R. A. Peacock, C.E.— In this 

 paper the author brings forward a great number of details, derived 

 in part from personal observations and in part from ancient 

 documents, to prove that a considerable submergence of land has 

 taken place round the island of Jersey within comparatively 

 recent times. He referred principally to the existence of a sub- 

 merged forest in the Bay of St. Ouen, evidenced by the existence 

 of stumps of trees in the sea-bottom there, and by the traditional 

 fact that up to quite a late period fees were paid for privileges 

 connected with the forest of St, Ouen, althoiigh the forest itself 

 had long previously disappeared beneath the sea. From the 

 evidence it would appear that the submergence took place at the 

 end of the fourteenth or the beginning of the fifteenth century. The 

 author also noticed the occurrence of peat and submarine trees m 

 the little bay of Greve de Lecq on the north side of Jersey, and 

 especially referred to the evidence afforded by the Ecrehous rocks 

 and Maitre Isle, there having been in the latter a priory or chapel, 

 supported by rents derived from the parish of Ecrehous, which is 

 now represented only by a small islet, with the rums of an eccle- 

 siastical building upon it, and a range of rocks protruding but 

 little above the sea.— The physical conditions under which the 

 Upper Silurian and succeeding Paleozoic Rocks were probably 



