262 



NA TURE 



\J'an. 22, 1885 



midnight ... 9 ... 9 .. 19 ... 6 



Hence the maximum occurs on these heights shortly 

 after midnight, and the minimum shortly after noon. 

 Now it will be seen that these diurnal maxima and 

 minima occur nearer midnight and noon than do the phases 

 of the other meteorological phenomena, thus suggesting a 

 direct connection with solar and terrestrial radiation. It is 

 singular that, while the diurnal periodof strongest insolation 

 determines the occurrence of the maximum velocity of the 

 wind over extensive land surfaces, it determines the mini- 

 mum velocity on peaks rising to a great height above the 

 land surfaces surrounding them. Of special importance 

 in its bearings on the question is the curve of diurnal 

 variation on Ben Nevis for the three winter months of 

 18S3-84, when the mean velocity of the wind was nearly 

 double that of the summer months. In that season Ben 

 Nevis was under a deep covering of snow, the sky clouded 

 nearly the whole time, the air frequently darkened with 

 dense drifting fogs, and the difference between the mean 

 lowest and highest hourly temperature only half a degree. 

 Notwithstanding the practical uniformity of temperature of 

 the surface of the top of Ben Nevis during the twenty-four 

 hours of the day, the curve of the diurnal variation in the 

 wind's velocity was as clearly marked in winter as in 

 summer, and the two curves were alike in showing the 

 occurrence of the maxi mum shortly after midnight, and the 

 minimum shortly after noon. We must therefore conclude 

 that the pei uliar type of the diurnal curves of wind velocity 

 on these elevated peaks is altogether independent of the 

 temperature of the surfaces over which the winds blow. 

 The results point not obscurely to an investigation of the 

 relations of the visible and invisible vapour of the atmo- 

 sphere to solar and terrestrial radiation as an inquiry of 

 first importance in meteorology. 



OUR BOOK SHELF 



in Electrical and Magnetic Measurement. By 

 R. E. Day, M.A. New Edition. (London: Longmans, 

 Green, and Co., 18S4.) 



Mr. Day has produced a new and considerably improved 

 edition of a most useful and valuable little book. Every 

 teacher of electricity whose work is not confined to the 



beggarly elements of mere phenomena will thank Mr. 

 Day for the admirable selection of problems put together 

 in this volume. Nothing could be a greater boon to the 

 real student than the means thus afforded of testing his 

 knowledge of the exact quantitative laws of the science. 

 If it were not for the historic interest of that rather anti- 

 quated instrument — the torsion balance — we should doubt 

 the utility of giving so much attention to it. Although 

 the more modem electrometers have entirely superseded 

 the torsion balance as an instrument of research and of 

 measurement, it has, nevertheless, become so prominently 

 fixed — like some grand old fossil long ago extinct- 

 amongst the characteristic forms of electrical instruments, 

 that examiners still expect candidates for examination to 

 know something about it. On the other hand, the space 

 allotted to moments of torsion and inertia is all too brief, 

 though admirably filled. We must, however, take excep- 

 j tion to the practice apparently followed on p. 62, of 

 I expressing a moment of couple in dynes: it should surely 

 I be dyne-centimetres. The section on the chemical (or 

 I rather thermo-chemical) theory of electromotive force is 

 excellent. The problems comprised under the heading 

 I Electromagnetic Measurement are admirable, though 

 ; perhaps a little beyond most students. 



LETTERS TO THE EDITOR 

 [ The Editor does not hold himselj responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications . 

 [The Editor urgently requests cort espondents to keep their letters 

 as sliorl as possible. The pressure on his space is so great 

 that it is impossible otherwise to insure the appearance even 

 of communications containing interesting and novel facts. ] 



Earthquakes and Terrestrial Magnetism 



Mr. W. H. Preece having written to the Astronomer-Royal 

 to ask whether any disturbance of our magnets or our earth- 

 current apparatus was experienced during the recent earthquake 

 in Spain, it may be interesting to communicate also for the 

 information of your readers the result of an examination of oui 

 photographic registers in consequence made, and especially in 

 order that what has been remarked may, if possible, receive 

 confirmation. 



As respects magnetic movement, the magnets on Dec. 25 last 

 and following days were generally quiet. But on looking more 

 closely at the registers, attention was at once drawn to a small 

 simultaneous disturbance of the declination and horizontal force 

 magnets, occurring at 9I1. 15m. on the evening of December 

 25. Both magnets were at this time set into slight vibration, 

 the extent of vibration in the case of declination being about 2' 

 of arc, and in horizontal force equivalent to 'OOI of the whole hori- 

 zontal force nearly. The movements have not the character of 

 magnetic movements, and, if in reality produced by the earth 

 quake, are of course simply an effect of the shock, the magnets 

 being heavy bars suspended by silk threads some feet in 

 length. About ten minutes afterwards there is doubtful indica- 

 tion in the horizontal force register of a second disturbance. 

 There is no corresponding perceptible disturbance in the earth- 

 current registers. 



No other similar motion is observable either on December 25 

 or on the following days. 



It may be remarked that in Nature for January I last (p. 

 200) the time of occurrence of the earthquake at Madrid is said 

 to be 8h. 53m. p.m. Taking this to be Madrid time, it corre- 

 sponds to 9h. 8m. of Greenwich time. William Ellis 



Royal Observatory, Greenwich, January 15 



Teaching Chemistry 



The subject of science-teaching in schools, and more particu- 

 larly the best way in which practical chemistry should be taught, 

 has of late been discussed in the columns of Nature. With the 

 editor's leave, I should like to say a little regarding the methods 

 of teaching chemical science in general. 



NATURE for January S contained notes, by Profs. Sir H. E 



