2l6 



NA TURE 



{Jan. 15, 1874 



described with misty than with dry steam, and at each of which 

 the particles of water moving through the steam destroy energy 

 in creating eddies. Although not so obvious, the same is true 

 in tlie case of sound. The effect of waves of sound traversing a 

 portion of air is first to accelerate and then to retard it. And if 

 there are any drops of water in the air these will not take up the 

 motion of the air so readily as tlie air itself. They will allow the 

 air to move backwards and forwards past them, and so cause 

 friction and diminish the effect of the wave as it proceeds, just as 

 a loose cargo will diminish the rolling of a ship. He then pro- 

 ceeds to examine the relation between the size of the drops and 

 their effects, always supposing the same quantity of water to be 

 present. He says — I do not know that it has ever been noticed 

 whether a fine or a coarse mist produces the most effect on sound ; 

 it does not appear, however, that rain produces the same effect 

 as fog, and considering rain as a coarse fog we must come to 

 the conclusion that a certain degree of fineness is necessary. 

 If we examine theoretically into the relation between the size 

 of the drops and tlie effect they produce, always assuming 

 the same quantity of water in the air, we find in the first place 

 that if the air is subjected to a uniform acceleration, which acts 

 for a sufficient time for the drops to acquire their maximum 

 velocity through the air, the effect of the drops in a given time — 

 that is to say, the energy dissipated in a given time — is propor- 

 tional to the square root of the diameters of the drops. This 

 appears from the action of gravity. As previously stated, the 

 maximum downward motion of the drops, and hence the dis- 

 tance they wi'l have fallen in a given time and the energy 

 destroyed, is j .oportional to the square root of their diameters. 

 Hence where the acceleration acts continuously for some time, as 

 would be the case in a steam-iiipe, the effect will increase with 

 the size of the drops. This effect may be represented by a 

 parabolic curve in which distances measured irom the vertex 

 along the axis represent the size of the drops and the correspond- 

 ing ordinates represent their effect in destroying energy. If on 

 the other hand the acceleration alternates very rapidly then there 

 will not be time for the drop to acquire its maximum velocity, 

 and if the time be very short the drop will practically stand still, 

 in which case the effect of the droiJs will be proportional to the 

 aggregate surface which they expose. And this will increase as 

 the diameter diminishes, always supposing the same quantity of 

 water to be present. This latter is somewhat the condition 

 when a fog is traversed by waves of sound, so long as the drops 

 are above a certain size ; when, however, they are very small, 

 compared with the length of the waves, there will be time for 

 them to acquire their maximum velocity. So that starting from 

 drops the size of rain, their effect will increase as their size 

 diminishes, at first in the direct proportion, then more and more 

 slowly until a certain minuteness is reached, after which, as the 

 drops become still smaller, their effect will begin to diminish, at 

 first slowly, but in an increasing ratio tending towards that of the 

 square root of the diameter of the drops. This effect may be 

 represented by a curve which coincides with the previously 

 described parabola at the vertex, but which turns off towards the 

 axis, which it finally approaches as a straight line. This com- 

 pletes the investigation so far as I have been able to carry it. The 

 complete mathematical solution of the equations of motion does 

 not appear to be possible, as they are of a form that has not as 

 yet been integrated. However, so far it appears to me to afford 

 a complete explanation of the two phenomena, and further 

 to show, a fact not hitherto noticed, that for any note of 

 waves of sound there is a certain size of drop with which 

 a fog will produce the greatest effect. 

 Edinburgh 

 Botanical Society, Jan. 8. — The following communications 

 were read : — Obituary Notice of Dr. J. Lind-ay .Stewart, by Dr. 

 Cleghorn. — Note on a Station for Primula veris in Coldingham 

 Bay, Berwickshire, by Sir Robert Christison, Bart. — Notes of a 

 visit to Messrs. Dickson and Turnbull's Nurseries, Perth, with 

 remarks on arboricultural subjects, by James M'Nab, V.P. — 

 Note on the destruction by frost of seedling ash trees in Mr. 

 Robertson's nursery ground, near Fettes College, in May 1873, 

 by Alexander Buchan, M, A. —Notice of botanical excursions in 

 1873, by Prof Balfour.- Notes on some British fungi, by Prof 

 Dickson and Mr. John Sadler. Specimens were exhibited. 



Victoria 



Microscopical Society, Oct. 30, 1873.— Mr. W. H.Archer, 



the president, occupied tlie chair.— Mr. T. S. Ralpli addressed 



the society relative to a fungus affecting the rye-grass, which has 



been brought before the notice of the society. He regarded its 



botanical position as uncertain, but was inclined to think it be- 

 longed to a lower form of fungus than Ctavana. In a speci- 

 men which he had prepared, the mycelium or network of the 

 thread of the fungus would be observed penetrating the cells of 

 the lye-grass, thus robbing the cells of the materials intended 

 for the nourishment of the plant. These mycelial threads tra- 

 velled through the cells, and ultimately coming to the surface of 

 the leaf, produced the peculiarly reddish film which attracted the 

 eye of the observer, besides the withering of the leaf of the 

 plant. — Mr. F. Barnard exhibited some foramimfera, collected 

 from various parts of the colony and in Queensland, some of 

 which were unnamed and new to recent observers. — The Presi- 

 dent (Mr. Archer) brought forward living specimens of the polyp 

 Tyrcha inridis, and of some freshwater polyzoa, the latter being 

 apparently a new species, and allied to Fredericella, of which he 

 had found species in a pool on the banks of the Yarra. 



Paris 

 Academy of Sciences, Jan. 5 — M. Bertrand in the chair. 

 This being the first meeting of the year the members proceeded to 

 elect a vice-president. [.See Notes.] M.de Quatrefages, the retir- 

 ing president, then read his report, after which the Academy pro- 

 ceeded with its usual business — the following papers were read. 

 — On the conductibility of magnetic tensions, by M. Jamin. — 

 On a new and simple form of the pro-embryo of echinoderms 

 Stellerid."e [Aslcriicus Tciriiciilaltis), by M. H. de Lacaze- 

 Duthiers. A mechanical interpretation of the laws of Dulong 

 and Petit, and Wcestyn on specific atomic heats, by M. A. Ledieu. 

 This paper contained a number of mathematical data in relation 

 tothe recent papers of MM.Lockyer, Dumas, and Berthelot. — Re- 

 marks on the relations bet\\'een specific heats and atomic weights 

 in simple and compound bodies, by M. A. Pissis. The author 

 states that these relations tend to show that there is no distinc- 

 tion really existing between simple and compound bodies, but 

 that on the contrary the so-called elements behave to a certain 

 extent like binary compounds. — On ammoniacal urine, its 

 dangers, and the means of preventing it, by MM. Gosselin and 

 Robin. M. Pasteur observed in connection with this subject, 

 that it would be of great importance to ascertain if this cha- 

 racteristic of urine is not connected with the presence of 

 an organised ferment. — The perpetual secretary re.ad a note 

 from M. Poey on the connection between sun-spots, earth- 

 quakes in the Antilles and Mexico, and volcanic eruptions 

 throughout the world. — Researches on the conditions under 

 which a conoid of a given curve exhibits a contact of a deter- 

 minate order, by M. Painvin. — An answer to M. Faye's remarks 

 on terrestrial waterspouts, by M. Th. Reye. M. Faye made 

 some remarks in reply. — On the variable period in the closing of 

 a voltaic circuit, by M. A. Cazin. This was an answer to M. 

 Blaserna's remarks. — On the conditions necessary for the forma- 

 tion of octahedral borax, by M. de Gernez. — On the geological 

 conditions of the islands adjacent to the African shore from 

 Morocco to Tunis. — On a Marine Carboniferous flora discovered 

 in the neighbourhood of I'Ardoissiere in the valley of Lichon 

 (Forez). — On the geographical distribution of the ferns of New 

 Caledonia, by M. Eng. Fournier. — On the pluvial law of the torrid 

 zone, in the basin of the Atlantic Ocean, by M. V. Raulin. 



CONTENTS Page 



The Pollution of Rivers 197 



The Conservation of Energv 198 



Weberbauer's "Fungi of North Germany." By Rev. M. J. 



Berkeley, F.L.S 200 



OuK Book Shelf 201 



Letters to the Editor : — 



The Shrinking of the Earth and Terrestrial Magnetism.— H. H. 



HoWORTH 20I 



Vivisection. — G. W. Cooke 202 



Moraines.— J. J. Murphy, F.G.S 202 



Indian Snakes. — E. H. Pringle 203 



The use of Terms in Cryptogamic Botany 203 



Polarisation of Light, IIL By W. SroTTlswooDE, Treas. R.S. 



(IVi'i/t lllusiratio7i) 203 



On the Motion and Sensation of Sound, I. Royal Instituuon 



Christmas Lectures by Prof. Tykdall, F.R.S. (With JUustrations). 206 

 Scholarships and Examinations for Natural Science at Cam- 

 bridge. 1874 209 



Astronomical Almanacs 210 



Telegraphing Extraordinary 212 



Scientific Serials 214 



Societies and Academies 215 



Erratum. — VoL ix. p. 132, 1st col. line 19, for " Mr. J. D. Painter" read 

 '' Mr. J. D. Sainter." 



