September 9i i^97j 



NA TURE 



461 



majority of these organisms appear to be beneficial rather than 

 inimical to man. There is not time to attempt even a brief 

 description of all the " useful fermentations " due to bacteria, 

 but the following cases will point the conviction that a school of 

 bacteriology, which has nothing to do with medical questions, 

 but investigates problems raised by the forester, agriculturist, 

 and gardener, the dairyman, brewer, dyer, and tanner, &c., will 

 yet be established in England in connection with one or other 

 of our great botanical centres. 



{To be continued.) 



PHYSICS A T THE BRITISH ASSOC I A TION. 



'pHE meeting of the American Association at Detroit and the 



■'■ central position of Toronto have contributed greatly in 

 bringing together a large number of Canadian and American 

 mathematicians and physicists to meet their co-workers on this 

 side of the Atlantic. The opportunity thus afforded of con- 

 ference and exchange of ideas haS been one of the chief pleasures 

 of the meeting. 



It was universally felt that the presidential address of Prof. 

 Forsyth (pp. 374-378) formed a clear and eloquent exposition of 

 the claims of pure mathematics, and at its close Lord Kelvin, 

 in moving a vote of thanks, declared that any one in science 

 who could possibly choose would elect to belong to the mathe- 

 matical rather than the non-mathematical class. President 

 London, of the Toronto University, in seconding the vote, said 

 that the address was specially needed in Toronto, because the 

 public there had accused the university of attaching too much 

 importance to mathematics. 



Mr. J. A. Palerson, in a paper on the unification of time, 

 described the efforts made by several scientific societies in 

 Canada to secure uniformity in the specification of time by 

 astronomers, navigators and the public ; the suggestion being 

 that the day should commence and end at midnight, and the 

 hours be counted from o to 24. The proposal gave rise to some 

 discussion. Prof. Newcomb pointed out that navigators, making 

 observations usually at noon, found that time most convenient 

 as the commencement of the day, while astronomers for similar 

 reasons would choose midnight. Prof. Rticker gave an account 

 of the inquiries made by the British Royal Society, Foreign 

 Office and Admiralty, from which it appears that any inter- 

 national agreement is at present hopeless ; so that the Nautical 

 Almanac for 1901 will be compiled in the same manner as its 

 predecessors. 



Prof. Riicker exhibited photographic records of objective 

 combination tones, both summational and difference tones 

 having been obtained. In this research he was assisted by 

 Messrs. Forsyth and Sowter. The method and apparatus used 

 were the same as in the investigation of Prof. Riicker and Mr. 

 Edser — namely, the observation of interference bands produced 

 by the light reflected from a mirror carried by a resonant tuning- 

 fork ; the shift of the bands by the motion of the fork was, how- 

 ever, photographed on a moving sensitive surface, instead of 

 being observed by eye. 



An account of the work of the Committee on Seismological 

 Observations was given by its indefatigable secretary, Prof. 

 Milne. An examination of earthquake records seems to show 

 that sub-oceanic earthquakes and landslips are more frequent 

 than those on land, and that the Tuscarora deep is the origin of 

 many of them. The most important portion of the report is, 

 however, that relating to the rate of propagation of seismic 

 waves from their origin to various points on the earth's surface. 

 The records show that the velocity of propagation increases with 

 the distance travelled, so that most probably the wave goes 

 through the earth and not round its superficial crust, the speed 

 of transmission being greater in the interior than in the crust. 

 This, as Lord Kelvin pointed out, indicates that the moduli of 

 elasticity of the material of the earth's interior are greater than 

 those of the crust, possibly because of the higher pressure at 

 great depths. 



At the meeting of the section on Friday, Dr. N. E. Dorsey 

 described some careful experiments to determine the surface 

 tension of water by the method of ripples, the results of which 

 agree with those of M. Sentis, obtained by an entirely different 

 method. In the case of dilute aqueous solutions, the surface 

 tension obtained by this method is a linear function of the 

 concentration. 



NO. 1454. VOL. 56] 



Prof. Callendar and Mr. Barnes gave an account of their 

 new method of measuring the specific heat of liquid, by passing 

 an electric current through a fine tube through which a current 

 of the liquid flows. The experiment is continued until the tem- 

 perature-difference between the ends of the tube becomes 

 steady ; this temperature-difference and the rate of flow of the 

 liquid are then measured. Loss of heat by radiation is almost 

 eliminated by surrounding the tube with a vacuous chamber, and 

 small losses are allowed for. Another important communica- 

 tion on calorimetry was that of Profs. Ewing and Dunkerley on 

 the specific heat of superheated steam. Their method consists 

 in passing saturated steam through a porous plug, thus super- 

 heating it ; the results show that for 10° superheating at atmo- 

 spheric pressure the specific heat is about 0*44, while the ordi- 

 narily accepted value, 0*48, is only correct if the superheating 

 exceeds 25", as in Regnault's experiments. 



A crowded audience assembled to hear Lord Kelvin's paper 

 on the fuel-supply and air-supply of the world. He argued that, 

 as the earth was in all probability originally hot and liquid, no 

 primeval vegetable fuel existed ; further, no free oxygen existed 

 at that period, since it is not found in gases evolved from min- 

 erals or in the spectra of stars. Probably, therefore, the oxygerk 

 of the air has resulted from the action of sunlight on plants, and 

 as this oxygen would be furnished by 340 million million tons of 

 fuel, we have an upper limit to the amount of fuel in the world.. 

 On the other hand, the British Coal Supply Commission of 1831, 

 estimated the amount of available fuel in England and Scotland 

 to be 146,000 million tons, which is greater than the average for 

 the whole earth. It follows, then, that the oxygen of the atmo- 

 sphere resting over Britain is insufficient to burn up the fuel of 

 the country, and the cessation of life may possibly occur by 

 asphyxiation rather than want of fuel. In the discussion on this 

 paper Prof. Fitzgerald stated that, according to his calculations, 

 the sun's energy will support five persons to every square metre,, 

 so that there is no fear of life becoming extinct by failure of the 

 sun's energy, as some people have supposed. 



In spectroscopy. Prof. Runge stated that Prof. F. Paschen 

 and himself had succeeded in separating the spectrum of oxygen 

 into six series, two principals each having two subordinates, 

 the lines of one principal series and its subordinates being triple. 

 The importance of this paper lies in the fact that the oxygen', 

 spectrum is shown to be analogous to that of helium ; and a* 

 oxygen does not, so far as we know, contain a mixture of 

 elements, the idea that helium is a mixture has now been 

 abandoned. Profs. Runge and Paschen find also that the 

 spectra of sulphur and selenium each give a principal series of 

 lines and two subordinate series, but in each case one line 

 occurs which does not fit into any of the series, and which 

 may be the fundamental line of another series. Using the large 

 grating of the Johns Hopkins University, Mr. W. J. Hum- 

 phreys has succeeded in causing the lines in the arc spectra of 

 metals to shift appreciably by increasing the pressure of the 

 atmosphere surrounding the arc ; in all cases increased pres-- 

 sure causes the wave-length of the lines to increase, the lines, 

 move towards the red end of the spectrum. The shift is of 

 the same order of magnitude as the Doppler effect, but could 

 be distinguished from the Doppler effect in a celestial spectrum 

 by the fact that lines belonging to principal and subordinate 

 series are differently shifted by pressure, whereas they are all 

 displaced equally in the spectrum of a receding body. Dr. J. 

 Larmor has discussed the subject mathematically, and finds 

 that the displacement is of the same order as would be pro- 

 duced by change of specific inductive capacity of the air by 

 pressure. Prof. Schuster has photographed a metallic spark- 

 spectrum on a film moving rapidly at right angles to the slit 

 of the spectroscope ; the result shows that the air-lines flash 

 out for an exceedingly short time : the metallic particles,^ 

 however, remain luminescent for a much longer period with 

 gradually diminishing intensity. He was able to trace the 

 motion of the metallic particles from the electrodes to the middle 

 of the spark, and to measure their velocity, which ranged from 

 400 to 2000 metres per second. 



Prof. S. P. Thompson distinguished four varieties of kathode 

 rays, differing in their power of exciting fluorescence, exciting 

 X-rays, and deflexion by a magnet. The first kind is the 

 ordinary kathode ray ; the second kind is produced when kathode 

 rays have fallen on a surface and produced X-rays (they have 

 then lost their power of exciting more X-rays). The third variety 

 arises when kathode rays are passed through a negatively 

 charged metallic spiral or gauze-sieve ; they cannot be deflected 



