3 o8 



NATURE 



{July 27, 1882 



Local mean time. Sun's altitude. 

 h. m. s. 



First external contact, Dec. 6 ... 8 52 37 a.m. ... 30 15 



„ internal „ 9 13 23 a.m. ... 33 54 



Last internal ,, „ ... 2 39 5 p.m. ... 32 17 



,, external ,, ,, . .. 3 o 22 p.m. ... 28 29 



Wells' Comet. — The fallowing places of this comet are for 

 Greenwich midnight : — 



K.A. 

 h. m. s. 

 Jnly 27 ... II 39 1 .. 

 29 ... 11 44 41 .. 



3' ... " 5° 5 ■■ 



August 2 ... 11 55 14 .. 



4 ... 12 o 9 .. 



6 ... 12 4 51 .. 



8 ... 12 9 22 .. 



10 ... 12 13 43 .. 



12 ... 12 17 54 .. 



14 ... 12 21 56 .. 



Decl. Loir, distance from 



Earth. Sun. 



+ 5 5S7 ... 0-2614 ... OT3S0 



5 3 8 '3 ... '2732 ... -1506 



5 185 ... -2867 ... -1626 



4 59'3 ■•• '30°4 ... 'I74 2 



4 40-6 ... -3126 ... -1853 



4 227 ... -3244 .. -1960 



4 S"2 •■• -3358 - '2064 



3 48-2 ... -3469 ... -2164 



3 3 T 7 ••■ '3^76 ... "2260 



157 ... o- 3 6So ... 0-2354 



The calculated intensity of light on August 9 is equivalent to 

 that at the first Harvard College observation on March 19. 



Comet-seeking in the Southern Hemisphere. — From 

 a communication to the Sydney Morning Herald, we learn that 

 Mr. Tehbutt, of Windsor, N.S.W., the discoverer of the great 

 comet of 1861, has, at the instance of the Boston (U.S.) Scien- 

 tific Society, undertaken the organisation of a corps of amateur 

 comet-seekers in Australia, and with this object has addressed a 

 circular to several persons in the colonies, who have manifested 

 an interest in the science. We wish Mr. Tebbutt every success : 

 the matter could not be in better hands. It would be easy to 

 adduce numerous cases where the theories of these bodies have 

 -uffered from the want of southern observations, and it may be 

 hoped, that in conjunction with the systematic search undertaken 

 by a number of observers in America, and, we are glad to add, 

 i 1 this country also, it will he quite an exceptional case for a 

 comet within range of ordinary telescopes to escape detection, 

 as we know many have done in past years. The additions to 

 the number of comets of short period during the last fifteen years. 

 are alone a sufficient inducement to institute more systematic 

 examination of the heavens in future. 



PHYSICAL NOTES 

 An organ-pipe sonometer is described in the American Jour- 

 nal of Science, by Mr. Le Conte Stevens. The ordinary reson- 

 ance box of the sonometer is in this instance replaced by a double 

 organ-pipe of spruce fir-wood, tuned to give the noleC = I32 

 vibrations. Three steel wires are stretched above, two being 

 tuned to the fundamental, the other strained to various degrees 

 of tension by a lever and a sliding weight. There are also 

 arrangements for sharpening or flattening the note of one of the 

 pipes at will, so as to produce beats. By varying the wind- 

 pressure, the natural harmonics of the pipes can be produced. 

 The object of the instrument is to afford a convenient means of 

 producing the notes of the natural scale and those of the tem- 

 pered scale, by way of contrasting them with one another. The 

 apparatus has several other uses as a lecture instrument in 

 acoustics. 



M. Cailletet has invented a new pump for compressing 

 gases to a high degree of compression. The main point in its 

 construction is the method by which he obviates the existence of 

 useless space between the end of the piston-plunger and the 

 valve, which closes the end of the cylinder. This he accom- 

 plishes by inverting the cvlinder and covering the end of the 

 plunger with a considerable quantity of mercury. This liquid 

 piston can of course adapt itself to all the inequalities of form of 

 the interior space, and sweeps up every portion of the gas, and 

 presses it up a conical passage into the valve. The valve by 

 which the air enters the body of the pump is opened by a cam- 

 gearing after the descent of the piston below point where the 

 air rushes in. 



Another suggestion due to M. Cailletet is worthy of notice, 

 and is applicable to many pieces of laboratory apparatus beside 

 air-pumps. It is the employment of vaseline as a lubricant 

 wherever there is a liability of the presence of mercury ; for, as 

 is known, most oils and fatty matters clog with finely-divided 

 mercury, and are objectionable on this account. 



New forms of secondary battery continue to make their ap- 

 pearance, most of them btsed upon the accumulator of Plante. 



Mr. R. E. Crompton has lately patented a process, for giving'a 

 large effective surface to the leaden electrodes by making it 

 porous, by adding to the lead some other substance capable of 

 being extracted by the action of acid, or by heat, or by other 

 reagents. Another modification due to Messrs. Biggs and Beau- 

 mont, consists in collecting in a separate vessel the hydrogen or 

 other products of decomposition, in the accumulator, the col- 

 lected products being afterwards recombined as fast as required* 

 The electrodes in this case are composed of finely divided lead. 



We have also received a report of a lecture delivered by M. 

 Maurice Levy before the Societe d' Encouragement on the same 

 subject of electrical units. It speaks volumes for the mathe- 

 matical education given in the public schools of Paris, if an 

 audience of a society comparable to that of our Society of Arts 

 could follow the lecturer through a mathematical discussion 

 like that before us, which includes a discussion of the doctrine 

 of dimensional equations, and of the elimination of arbitrary 

 coefficients. M. Levy applauds the decisions of the Congress, 

 which he expounds lngically and elegantly. 



The following experiment of Messrs. Jamin and Maneuvrier 

 illustrates the presence of an inverse electromotive force in the 

 voltaic arc, dependent on the actions therein excited by the 

 current. A continuous current was passed first from coke to 

 mercury, producing a reddish coloured arc. The current was 

 then reversed, when the arc appeared green, and the metal 

 volatilised rapidly. Then the current of an alternating Gramme 

 machine was passed through the same arrangement. The arc 

 now appeared green, showing a predominance of the current 

 from mercury to coke, although in ordinary circumstances the 

 two alternately directed currents are absolutely equal in strength. 



The decisions of the Electrical Congress have ar -used the 

 electricians of several Continental nations to realise the advance 

 in exact science which the adoption of a uniform system of 

 electrical units implies ; and not to be behindhand, they are 

 striving to spread a knowledge of what has been done. The 

 new determination which is to he made of the value of the ohm 

 has furnished material for several discussions, in which it is 

 curious to observe the suggestions that were brought forward as 

 new. Others content themselves with expounding that which 

 has been already done. We have before us, from the pen of 

 Dr. Guglielmo Mengarini, assistant in the Physical Institute of 

 the University of Rome, a " History of the Electromagnetic 

 Unit of Resistance," reprinted from the official bulletin of the 

 Minister^'sif Public Instruction. Beginning with the work of 

 Davy, Becquerel, Ohm, ar.d Wheat-tone, the author describes 

 how gradually the rheostat brought forth the resistance-coil, and 

 the units of Siemens and of the British Association. He then 

 gives a theoretical discussion of the absolute electromagnetic 

 unit of resistance, and an account of the methods of Weber and 

 of the British Association for determining it. The main points 

 in the propositions submitted to the International Congress at 

 Paris in 1S81 are then given, together with the formal decisions 

 of the Congress thereupon. 



A valuable contribution to the subject of the electricity of 

 flame has been lately made by Herren Elster and Geitel ( IVied. 

 Ann. No. 6). The discrepancies in previous results are attri- 

 buted largely to the behaviour of the air layer immediately outside 

 of the flame having been left out of account. The authors used 

 a Thomson quadrant electrometer for measurement. They find 

 the supposed longitudinal polarisation of flame merely apparent, 

 and due to unequal insertion of the wires u-ed as electrodes. On 

 the other hand, flame is strongly p darised in cross section ; an 

 electrode in the air about the flame is always positive to one in 

 the flame. The theory the authors adopt is this : — By the process 

 of combustion per se free electricity is not 1 roduced in the tlame ; 

 but the flame-gases and the air-envelope have the property of 

 exci ing, like an electrolyte, metals or liquids in contact with 

 them. To this electrolytic excitation is added a thermo-electric, 

 due to the incandescent state of the electrodes. The amount and 

 nature of the electric excitation is independent of the size of the 

 flame, and dependent on the nature, surface-condition, and glow 

 of the electrodes, and on the nature of the burning gases. Inter 

 alia, it is remarked that flames may be combined in series like 

 galvanic elements, and so as to form a " flame-battery." 



In a recent dissertation (IVied. Ann. No. 7), llerr Heine 

 describes experiments on the absorption of heat by gas-mixtures 

 with varying percentage of constituents, and he thence deduces a 

 method of ascertaining the amount of carbonic acid in the air. 

 Varied mixtures of CO s and air, in known proportions, were 



