2l6 



NA rURE 



\Pec. 29, 1887 



At the upper end the brass cylinder has a lateral opening by 

 which its interior can be connected with an india-rubber aspirat- 

 ing ball. The chief difficulty met with was in the construction 

 of a suitable valve for the aspirating ball. Finally he succeeded 

 in making a valve such that no air was ever driven back towards 

 the thermometer when the ball was compressed, but only drawn 

 over the bulb of the instrument during the aspiration at the rate 

 of '2 to 2'5 metres per second. Within these limits the rate at 

 which the air is drawn over the bulb had no influence on the 

 temperature recorded by the thermometer. Of extreme import- 

 ance, as showing the suitability of the instruments, were the 

 speaker's observations on the temperatures recorded by two of 

 his thermometers, of which one was exposed to the direct rays of 

 the sun, while the other was shaded by a distant shutter : the 

 two thermometers recorded the same temperature, while at the 

 same time an actinometer exposed to the sun showed a tempera- 

 ture 17° C. higher. The same exactness in the determination of 

 the humidity of the air is obtained when a pair of these thermo- 

 meters is used, and the bulb of one is wrapped round with a 

 piece of moist cloth. This instrument is specially suitable for 

 observations in a balloon. The speaker explained that only 

 shortly before the present meeting he had found that a similar 

 instrument had been constructed by Welsh about the year 1850. 

 — Dr. Robert von Helmholtz gave an account of experiments 

 which he had carried on conjointly with Dr. Sprung with a view 

 to determining the humidity of the air. They had both arrived, 

 independently of each other, at the idea that the determination 

 of the dew-point might best be made, not, as in the usual way, 

 by the condensation on the bulb of a thermometer, but by 

 measurement of the amount of rarefaction which the air must 

 undergo in order that a mist may be produced. In a previous 

 research the speaker, when determining the vapour-tension over 

 solutions of salts, had compressed the air in a closed space, and 

 then obtained a formation of mist by suddenly reducing the 

 pressure again to that of the atmosphere. By determining the 

 general excess of pressure which is thus requisite, the dew- 

 point may be determined. Dr. Sprung has compared the 

 dew-point as thus determined and as obtained by Regnault's 

 apparatus. The experiments are not yet carried sufficiently far 

 to yield any numerical results, but even now it may be said that 

 this new method of determining the dew-point is extremely 

 trustworthy. 



Physical Society, December 9. — Prof, du Bois Reymond, 

 President, in the chair. — Dr. Badde developed the mathematical 

 formulas by means of which he can determine the vibrational 

 condition not only of a vibrating string, but also of a square 

 plate— formulas which make it possible to determine the relation 

 between the pitch of the note and the vibration -amplitude of the 

 vibrating plate. — Dr. Pringsheim gave an account of the experi- 

 ments he has made, in conjunction with Dr. Summer, to de- 

 termine the quotient {k) of the specific heat of gases. The value 

 of k is determined either by measuring the rate of propagation of 

 sound in gases which obey Mariotte's law, or else from the ratio 

 of temperature to pressure when the volume is kept constant. Up 

 to the present time the rate of transmission of sound has not been so 

 exactly determined that the values can be used for deducing the 

 value of k. Similarly the second method has as yet given very 

 discordant results, while at the same time the experiments have 

 not been free from errors. Drs. Pringsheim and Summer have 

 compressed air in a glass balloon whose capacity was sixty 

 litres, and determined its temperature by means of a fine silver 

 wire passing through it whose electrical resistance was known. 

 Hereupon the pressure in the balloon was allowed to sink to 

 that of the atmosphere by opening a tap leading into it, and the 

 cooling thus produced measured by means of the wire. Imme- 

 diately upon this the tap was again closed, the air becoming 

 warmed by the heat which passed into it from the air surround- 

 ing the balloon, and the rise of temperature again measured. 

 During these experiments it was found to be of no consequence 

 whether the rarefaction of the compressed air took place rapidly 

 through a tap with a large bore, or through one with a narrow 

 aperture ; the wire always showed the same amount of cooling, 

 thus proving that it follows the alteration of temperature of the 

 air very rapidly. Similarly the length of the wire was found to 

 have no effect on the results, thus showing that the temperature 

 of the surroundings has no influence on the temperature recorded 

 by the wire. The resistance of the wire was determined by the 

 bridge-method, partly by means of a galvanometer, partly by 

 means of a telephone. The ratios of the alterations in resistance 



of the wire to alterations of temperature were determined, within 

 the necessary limits, for several fine wires. The speakers con- 

 sidered that the only objection which can be raised to their 

 experiments is that the above determination was not made 

 with the same wires which were used in their experiments, and 

 they propose to do away with even this objection by some later 

 experiments which have not as yet been carried out. All other 

 possible objections have been set aside by varying the conditions 

 of their work while ^obtaining constant results. As a mean of 

 the sepat-ate measurements rthey obtained as a value for k the 

 number i'384 ; the deviation for the mean value amounted only 

 to a few hundredths per cent. The above value for k cannot 

 however be taken as being absolute until it has been proved that 

 there is a proportionality between the temperature and resistance 

 of the silver wire which thev used in their experiments. 



BOOKS. PAMPHLETS, and SERIALS RECEIVED. 



Ferrets and Ferreting, 2nd edition (U. Gill). — Massachusetts Insti- 

 tute of Technology : 23rd Annual Catalogue of the Officers and Students, 

 &c. (Boston). — Die Theekultur in British-Ost-Tndien ; Hist. Naturwissen- 

 schaftlich und Statistich (Prag). — Quarterly Journal of the Royal Meteoro- 

 logical Society, October (Stanfjrd). — Annalen der Physik und Chemie, 1887, 

 No. 12 (Leipzig). — Archives Itahennes de Biologie, to.-ne ix. fasc. i (Turin). 

 — Journal of the Royal Microscopical Society, December (Williams and 

 Norgate).— Elementary Text-book of Physiography : W. Mawer (Marshall). 

 — Management of Accumulators, 3rd edition : Sir D. Salomons (Whittaker). 

 — Sewage Treatment, Purification and Utilization : J. W. Slater (Whittaker). 

 —Flour Manufacture : F. Kick, translated by H. N. P. Powles (Lock- 

 wood). — Photography Simplified, 3rd edition (Mawson and Swan). — Trans- 

 actions of the Sanitary Institute of Great Britain, vol. viii. (Stapford). — A 

 Treatise on Chemistry, vol. iii. Part 4, Organic Chemistry : Roscoe and 

 Schorlemmer (Macmillan). — Present Religion, Part 2 : S. S. Hennell 

 (Triibner). — Die Aitchnftliche Fresko und Mosaik-Malerei : Dr. O. Pohl 

 (Leipzig). — Recherches sur I'lso'ement du Fluor: H. Moissan (Gauthier- 

 Villars, Paris). — Journal of Physiology, vol. viii. No. 6 (Cambridge). — 

 Morphologisches J.ihrbuch, xiii. Band, 2 Heft (Williams and Norgate). 



CONTENTS. PAGE 



The Rosicrucians 193 



The Mechanics of Machinery. By Prof. A. G. 



Greenhill 195 



The Solomon Islands 196 



Crown Forests at the Cape of Good Hope .... 198 

 Our Book Shelf :— 



Denslow and Parker : " Thomas A. Edison and 



Samuel F. B. Morse" I99 



Wright: " Sound, Light, and Heat " 199 



Layard : " Through the West Indies " 199 



Letters to the Editor : — 



" The Conspiracy of Silence." — Samuel F. Clarke ; 



An Old Pupil of Wy ville Thomson's .... 200 

 Greenland Glaciers. — Prof. Joseph Prestwich, 



F.R.S 200 



"The Mammoth and the Flood." — Henry H. 



Howorth, M.P. ; Your Reviewer . . . , . 200 

 Centre of Water Pressure. — George M. Minchin . 201 

 The Recent Earthquakes in Iceland. — -Th. Thorodd- 



sen 201 



The Canary Islands. — Olivia M. Stone 201 



The Ffynnon Beuno and Cae Gwyn Caves. — Dr. 



Henry Hicks, F.R.S 202 



Distorted Earth Shadows in Eclipses. — Capt. Henry 



Toynbee 202 



Dr. Balfour Stewart, F.R.S. By Prof. P. G. Tait . 202 

 Christmas Island. By J. J. Lister; Capt. W. J. L. 



Wharton, F.R.S 203 



Timber, and some of its Diseases. II. {Illustrated.) 



By Prof. H. Marshall Ward 204 



Notes 207 



Astronomical Phenomena for the Week 1888 



January 1-7 210 



Geographical Notes 211 



Journal of the Royal Agricultural Society. By Prof. 



John Wrightson . , 211 



The Reproductive Organs oi Alcyonidium gelati'nosum. 



By Prof. W. A. Herdman 213 



Societies and Academies 213 



Books, Pamphlets, and Serials Received 216 



