yum 7, 1877] 



NA TURE 



115 



In working out the result it will be most convenient to use 

 consistently the C. G. S. system. On this system of measure- 

 ment the pressure employed was gl x 9S1 degrees per square 

 centimetre, and therefore the work expended per second in gene- 

 rating the waves was 196 X 9i X 9S1 ergs. Now the mechanical 

 value of a series of progressive waves is the same as the kinetic 

 energy of the whole mass of air concerned, supposed lo be 

 moving with the maximum velocity of vibiation (;•) ; so that, if 

 S denotes the area of the wave-front considered, a be the velocity 

 of sound, and p be ihe density of air, the mechanical vahie of 

 the waves passing in a unit of time is expressed by :; S . .7 . p . 1"-, 

 in which llie numerical value of a is about 34,100, and that of p 

 about '0013. In the present application S is the area of the 

 surface of a liemisphere, whose radius is 82,000 centimetres ; and 

 thus, if the whole energy of the escaping air were converted 

 into sound, and there were no dissipation on the way, the value 

 oiv at the distance of 82,000 centimetres would be given liy the 

 equation — 



,, _ 2X 196X 94X981 



whence 



27r(,82000)- X 34100 X 0013 

 : '0014 centimetres per second. 



This result does not require a knowledge of the pitch of the 

 sound. If the period be t, the relation between the maximum 

 excursion .v and the maximum velocity v is 



In the present case the note of the whistle was J '", with a fre- 

 quency of about 2730. Hence 



2x X 2730 

 or the amplitude of the aerial particles was less than a ten 

 millionth of a centimetre. 



I am inclined to think that on a still night a sound of this 

 pitch, whose amplitude is only a hundred millionth of a centi- 

 metre, would still be audible. 



Linnean Society, May 24. — Annual General Meeting. — 

 Prof. AUman, P". R.S., president, in the chair. — The Senior 

 Secretary (Mr. Currey) read his report, among other items, 

 mentioning that twelve fellows and five foreign members had 

 died enuring the past year. On the other hand forty-three 

 lellosis, three foreign members, and one associate had been 

 elected. Of active scientific workers that had passed away, J. 

 Scotc Bowerbank, Edward Newman, and Alfred Smee crllcd 

 for special mention ; the labours of the first named, in a pte- 

 viou>ly little-worked department, the sponges, marking an epoch 

 in British natural history. A passing tribute was due to the 

 memory of the foreign members that had died during the year, 

 for von Baer, Braun, De Notaris, Ehrenberg, and Hofmeister 

 in their several departments worthily represented biological 

 science in its broad aspects. — Mr. Gwyn Jeffreys, tieasurer, in 

 his financial statement, showed an increased balance in favour of 

 the Society, and this, notwithstanding extra outlay in valuable 

 additions to the library, improvements in the Society's scientilic 

 publications, &c. The demise of the late Charles Lamheit, 

 F.L.S., had brouaht the handsome bequest of 500/. to the funds 

 of the Society. — The president and officers were re-elected and 

 tlie following gentlemen, viz., Lieut.-Col. Grant, C.B. , W. 

 Carruthers, R. Hudson, Dr. J. Millar, and Dr. R. C. A. Prior 

 were elected into council in lieu of the subjoined, wlio retired 

 by rotation : — G. Bentham, Gen. Scott, C.B., R. B. Sharpe, 

 H. T. Slaiuton, and C. Stewart. We elsewhere give an abstract 

 of the presidential address, devoted to a resttiiie on "Recent 

 Researches among the Lower Sarcode Organisms," a subject of 

 daily increasing interest. 



Meteorological Society, May 16. — Mr. II. S. Eaton, M.A., 

 president, in the chair. — Messrs. Stephen Bietton, J. Gulson 

 Burge s, David Milne Home, and F. Gartside Tippinge were 

 elected fellows of the Society. — The following papers were 

 read : — .\n improved form of mercurial barometer, by Mr. R. K. 

 Power, F.M.S. The improvement consists in the use of a 

 double column of mercury, so that in the event of a vacuum 

 being formed by the escape of some mercury into the ci:>tern, the 

 shock is no longer felt by the tube but in the first place is re- 

 ceived by the mercary alone and then reflected much diminished 

 into the cistern, where it is modified by the presence of the 

 atmosphere. At the same lime, owing to the peculiar construc- 



tion of the cistern, the probability of any mercury leaving the 

 tubes is much less than in the case of the standard barometers at 

 present in use. It is also lielieved that the employment of the 

 double tube will do away with the necessity of boiling the mer- 

 cury. — The relation between the upper and under currents of the 

 atrnosphere around areas of barometric depresnon, by the Rev. 

 W. Clement Ley, F.M.S. This paper gives a description of the 

 mean directions of the movements of cirrus clouds over the dif- 

 ferent segments of areas of depression. The subject is treated 

 on its observational side, as it is not yet considered ripe for much 

 theoretical discussion, but one or two points seem likely to throw 

 some light on iho theory of the nioveaients of the atmosphere. 

 The direction of the upper currents round a depression is found 

 to be most intimately related to the direction in which the de- 

 pression itself is progressing. In the re.ir of a depression where 

 the mean direction of the surface winds is nearly parallel to the 

 isobars, or at right angles to the radius, the cirrus current almost 

 coincides with the surface wind, except near the central calm. 

 In the front of the depression on the other hand, where there is 

 the greatest indraught near the earth's surface, the upper currents 

 flow greatly away from the centre. The current in the rear of 

 a depression has therefore the greatest, and that in the front the 

 least vertical depth. The majority of our depressions travel 

 towards some point between N. and E., and so far as the 

 author has been able to calculate, the mean height of our south- 

 easterly winds is not half that of our north-westerly winds, even 

 supposing the latter to extend no h'gher than the stratum of 

 cirrus. The angle of deviation increases with the increase of 

 friction ; and it is possible, therefore, that the great incurvation 

 of the surface winds in the front of a depression is closely related 

 to the greater amount of friction which they encounter, for they 

 are comparatively shallow currents, and experience resistance 

 above as well as at their base. The contrast between the upper 

 currents on the right and those on the left of the trajectory is 

 quite as remarkable as that between the upper currents in the 

 front and in the rear, and it is very constant and well-marked in 

 its general character. As regards the centre, the upper-current, 

 when traceable over this district, commonly coincides, or very 

 nearly, with the wind previously felt at the earth's surface. — 

 Contributions to the meteorology of the Pacific — the Island of 

 Rapa, by Robert H. Scott, F.R.S. Rapa is a small island, 

 eighteen miles in circumference, in the South Pacific, in latitude 

 27° S. and longitude 144° W. The observations were made by 

 Capt. D. E. Mackellar, on board the depot ship Medas, during 

 the period extending from 1867, December 15, to 1869, May 27. 

 The climate appears to be an equable one. 



Physical Society, May 2fi. — Prof G. C. Foster, president, 

 in the chair. — The. following were elected members of the So- 

 ciety :— Lieut-Cob A. C. Campbell, Dr. H. Debris, F.R.S., 

 Mr. W. T. Thiselton Dyer, M.A., B.Sc, \V. Jack, M.A., and 

 Capt. Sale, R.E. — Lieut. -Colonel Campbell explained and exhi- 

 bited a double slit which he has employed for measuring the 

 distances between the lines in the spectrum and finds of great 

 service in cases where the illumination is so slight as to preclude 

 the possibility of using the ordinary miciometer. One slit 

 remaining stationary the other can be moved at rght angles to 

 its direction by means of a veiy delicate micrometer screw of 

 200 threads to the inch, the graduated head of which is capable 

 of distinctly indicating one-five-niillionth of an inch in the mo- 

 tion of the slit. If now a reading of the micrometer be taken 

 when tire slits are superposed and form one continuous slit, and 

 a second reading when any given line has been superposed upon 

 any other line at a moderate distance from ir, the difference be- 

 ti^een these readings will enable us at once to ascertain the dis- 

 tance between the lines if the micrometer be calibrated in leims 

 of the spectrum as seen in the observing telescope. The author 

 has made several measurements with this apparatus, .and finds it 

 to be capable of extreme accuracy, but it is of course essential 

 that the movable slit remains within a moderate distance of the 

 axis of the collimator. He then described a simple arrange- 

 ment for automatically fixing a prism, when placed on the table 

 of a goniometer at the angle of minimum deviation when dif- 

 ferent coloured rays are under examination. To the arms which 

 support the telescopes of the goniometer are attached two short 

 links of equal lengths connected at their extremities with a 

 nut sliding freely on an arm wh'ch is fixed radially to the 

 centre table of the instrument. The prism is held on this 

 table with its base at right angles to this arm, and it thus 

 remains adjusted for all the rays of the spectrum. — Mr. O. J. 

 Lodge then read two papers by Profs. Ayiton and Perry, jointly, 



