420 



NATURE 



{March 23, 1876 



a Bunsen burner, first, when ia its ordinary condition, and after- 

 wards with the air openings at the base closed. It was shown 

 that, whereas in tlie first case tlie effect produced was equivalent 

 to three divisions of the scale, in the latter case one- tenth of the 

 current produced by the exposure deflects the needle to the end 

 of the scale. Prof. Johnstone Stoney then explained the theory 

 which he has suggested in explanation of the phenomena observed 

 in the radiometers of Mr. Crookes, which has been published in 

 the Philosophical Magazine for the current month. The theory 

 rests on the supposition that there is an excessively small trace of 

 residual gas in the sphere in which the moving discs are enclosed. 

 When the apparatus is exposed to heat the blackened side of 

 the disc is slightly warmed, and this warms a layer of air in con- 

 tact with it. At the ordinary atmospheric pressure. Prof. Stoney 

 assumes the layer so warmed to have the thickness of a sheet of 

 paper, when the temperature of the disc is 20° C. above that of 

 the surrounding air, and on such a supposition we may calculate 

 it for any other pressure and temperature. If we diminish the 

 pressure the thickness varies inversely as the pressure raised to 

 the power |. Thus if the disc be raised xV° C. above the sur- 

 rounding air, and the exhaustion carried to the XT^TrTrth of an 

 atmosphere, the layer will have a thickness of more than a deci- 

 metre, and the effect of the air will then be peculiar. If the gas 

 is of such a density that the glass envelope is beyond the range 

 of this action, the gas beyond the limiting distance wJl be cold, 

 but if the effect reach the glass, conduction will take place to it. 

 There will then be a procession of warm molecules towards the 

 glass, where they will be cooled down, and form a number of 

 cold, slow-moving molecules, which will go back to the disc and 

 beyond it. And these processions will be intermixed with mole- 

 cules taking no part in the action. In consequence of this, very 

 few members will travel far in their paths ; a portion of the 

 motion of each, however, will be carried forward in the 

 right direction. So long as these processions go on, the 

 slow-moving molecules which reach the front of the disc 

 are thrown off more vigorously than from the back. Prof. 

 Stoney considers the pressure thus produced to be that mea- 

 sured by Mr. Crookes. With a pressure of the gas of 

 j^L^th of an atmosphere, an elevation of temperature of iV° C. 

 will produce the force actually observed, while if the exhaustion 

 be carried to i^inrxnrth the elevation of temperature necessary 

 will be iV C. Thus with the greater pressure a lower tempe- 

 rature will sufftce, but other influences, will then be brought into 

 play tending in an opposite direction. It was pointed out that 

 on this theory the action may be considered as closely resembling 

 electricity, and Mr. Crookes has shown that the glass envelope 

 is often itself slightly electrified. 



Paris 

 Academy of Sciences, March 13. — Vice-Admiral Paris in 

 the chair. —The following papers were read : — Observations of 

 the moon made with meridian instruments of the Paris Observa- 

 tory during 1875, by M. Leverrier. — Second note on the trans- 

 formation of nautical astronomy, through the progress of chrono- 

 metry, by M. Yvon Villarceau. — Observations of temperature at 

 the Mus.um during 1875, with electric thermometers placed at 

 depths of I to 36 metres in the ground ; and rhume of ten years' 

 observations, by MM. Becqucrel. This resume shows that the 

 mean annual temperatures of the ten years increase regularly 

 from I to 36 metres, at the rate of about one degree per 30 or 

 31 metres difference of level. An aquiferous sheet of 26 

 metres gave a slight excess of temperature. At 36 metres 

 the temperature was constant and equal to I2°'42 (mean 

 temperature at i metre = n°-3i).— On the siliciuration of 

 platinum and of som.e other metals, by M. Boussingault. — 

 On the flood of the Seine in February and March 1876, by 

 M. Belgrand.— Observations on M. Resal's recent communica- 

 tion on steam -jacketing of engine cylinders, by M. Ledieu.— Note 

 on water-pipes, by M. Boileau.— On the linear equations of the 

 second order, of which the integrals are algebraic, by M. Jordan, 

 —On the transit of Venus of Dec. 9, 1874, by M. Andij. The 

 diameter of a star (of sufficient brightness) varies with the aperture 

 of the instrument with which it is observed ; the author verified this 

 experimentally, and he draws some inferences relative to the 

 transit observations.— On the eggs of Phylloxeras, by M, Lich- 

 tenstein. — On a process of direct application of sulphide of 

 carbon in the treatment of phylloxerised vines, by M. Allies. — 

 Treatment of phylloxerised vines with sulphide of carbon intro- 

 duced and diffused in the soil by means of an aspirating appa- 

 ratus, by MM. Crolas and Jobart. An iron tube, with terminal 

 apertures, is inserted in the ground ; air is drawn off through it 



by a pump, while sulphide of carbon is sprinkled over the sur- 

 face ; thus the vapour penetrates the soil. The cost is 320 francs per 

 hectare. — On the employment of potash and of lime in treatment of 

 the vine, by M. Demaille. — On the overthrow of the'Grand-Sable 

 at Salazie, by M. Velain. The case was strictly analogous to that 

 of landslips in Switzerland (not a volcanic phenomenon). — On a 

 means of preservation against the accidents caused by fire-damp in 

 mines, by M. Minary. The gas, being lighter than air, ascends, and 

 M. Minary would make a series of vertical excavations in the roof to 

 receive it, the apertures merely allowing the gas to enter and the air 

 to escape. The collected gas could be drawn off to the surface by 

 pipes. Should the gas in these reservoirs be largely mixed with 

 air, he would place in them a system of porous tubes to separate 

 it by endosmose, and these would be connected with the suction 

 pipe.- — Letter from M. Peters on the discovery of the planet 

 ( 1 60) communicated) by M. Le i,Verrier. — ■ Observation of the 

 planet (160) made with the garden equatorial, by MM. Henry.-- 

 Observations of same planet at the Observatory of Marseilles, by 

 M. Borrelly. — On the approaching return to perihelion of the 

 periodic comet of D' Arrest, by M. Leveau. — On polar auroras, 

 by M. Plante. When the positive electrode of a strofig second- 

 ary battery is brought towards the liquid surface of a vessel of 

 salt water in which the negative electrode dips, you obsei^ve, 

 according to its distance from the liquid, a corona of luminous 

 particles round the electrode, or an arc bordered with a fringe 

 of bright rays, or a sinuous line which rapidly bends to and fro on 

 itself; the latter being especially similar to what one observes in 

 auroras (like the undulation of drapery moved by the wind). 

 Purple and violet tints appear as well as yellow. The liquid 

 is greatly agitated, and steam rises more abundantly the further 

 the electrode penetrates. Sound and magnetic perturbations 

 are had, like those accompanying auroras. The negative elec- 

 trode did not give the above phenomena, and auroras are pro- 

 bably due to a flow of positive electricity. Probably the 

 imperfect vacuum in the upper regions plays the part corre- 

 sponding to the negative electrode in the experiments, and the 

 electricity comes from tropical regions. — Source of carbonic 

 oxide, characteristics of formines, and of polyatomic alcohols, by 

 M. Lorin. — On the canga of Brazil, and on the basin of fresh 

 water at Fonseca, by M. Gorceix. Canga is a ferruginous con- 

 glomerate formed (according to the author) from debris of itabi- 

 rites carried down by water, and cemented by ferruginous water. 

 — On the causes which have brought about the retreat of glaciers 

 in the Alps, by M. Gruner. From meteorological observations 

 at St. Bernard, he finds that the period 1861-74, compared with 

 the previous twenty years, shows an increase of mean tempera- 

 ture of o°'92, a diminution of water of 0'204m., and, especially, 

 a reduction of one-half in the falls of snow, 4"846m. instead of 

 lom. At Geneva, a similar change has been peiceptible. — M. 

 Cagnant called attention to a bed of kaolin at Saint Beaudelle, 

 in the department of Mayenne. It would be well suited for 

 manufacture of sulphate of alumina, which could be used fo." 

 clarifying the Paris sewage water. 



CONTENTS Pack 



French and Swiss Troglodytbs 401 



The BoTHKAMP Sun Observations By Dr. Arthur Schuster . 402 

 Our Book Shelf :— 



Bennett's "Absorptive Glancis of Carnivorous Plants" .... 403 



Calderon's " Volcanic Rocks of the Canaries" 403 



Letourneau's " Biologic " 404 



Loudon's " Algebra for Beginners " 404 



Lhtters to thk Editor : — 



Coloured Solar Halos. — Dr. E. Frankland, F.R.S 404 



On the Evidences of Ancient Glaciers in Central France.— Prof .A. 



VON Lasaulx 404 



The Uintathenum. — Prof. W. H. Flower, F.R.S 404 



Morell's " Euclid Simplified," — J. R. Morell 405 



"Weight" and " Mass."— J. J. Walker 405 



The River-beds of the Riviera.— K. E. Bartlett 406 



The Ocelli in Insects. — C 406 



The Recent Storm.— T. S. Usborne 406 



Our Astronomical Column : — 



Struve's Companion of Procyon 4°^ 



The Total Solar Eclipse of 1883, May 6 406 



The Minor Planets 407 



On the Action of Light o.v Selenium 407 



The Late Col. Strangb, F.R S 408 



Huntbrian Lectures on the Relation of Extinct to Existing 



Mammalia, V. By Prof. Flower, F. R.S 409 



Prof. Huxley's Lectures on the Evidence as to thb Origin of 



Existing Vertebrate Anlmals, II 4«» 



Physical Science in Schools. By Rev. W. Tuckwell ; Dr. 



Andrew Wilson ; W. N. Hartley 4" 



Notes . . 4^3 



Report of the Cambridge Studies' Syndicate 415 



Scientific Serials ■ 4>7 



SOCIBTIBS AND ACADEtf IBS ............ i , • 4»» 



