Jan. 30, 1879] 



NATURE 



293 



the whole earth cannot be retarded exactly as though it 

 •were a rigid body. Now the tidal protuberance has not 

 this required fonn, and therefore there results a slow 

 secular distortion of the earth arising from the unequal 

 distribution over the surface of the forces which con- 

 stitute the tidal frictional couple. 



The greater part of the pull which retards the rotation 

 is applied in the equatorial regions, and therefore the 

 rotation of those regions will be more rapidly retarded 

 than that of the polar regions. As the earth's rotation is 

 from west to east, it follows that the polar regions will 

 outstrip the equator and will move very slowly from west 

 to east relatively to the equatorial parts. 



The exact mathematical solution for this kind of a 

 distortion of a viscous spheroid shows that it consists in 

 a simple cylindrical motion round the axis of rotation, 

 each point moving from east to west with a linear velocity 

 proportional to the cube of its distance from that axis. 



The distortion of the surface of the globe consists of a 

 motion in longitude from west to east, relatively to a 

 point in the equator, the rate of change of longitude 

 being proportional to the square of the sine of the 

 latitude. 



Numerical calculation shows, however, that in the later 

 stages of the earth's history (the development being sup- 

 posed to follow the laws found in the paper on " Preces- 

 sion " ) the distortion must have been very small. With 

 a certain assumed viscosity it is found that, looking back 

 45,000,000 years, a point in latitude 60° would lie 14' 

 further east than at present. From this it follows that 

 this cause can have had little or nothing to do with the 

 crumpling of geological strata. 



As, however, the distorting force varies inversely as the 

 sixth power of the moon's distance, it seems possible 

 that in the very earliest stages this cause may have had 

 sensible effects. It is therefore noteworthy that the 

 wrinkles raised on the surface would run north and south 

 in the equatorial regions, with a tendency towards north- 

 east and south-west in the northern hemisphere, and 

 north-west and south-east in the southern one. The 

 intensity of the distorting force at the surface varies as 

 the square of the cosine of the latitude. 



An inspection of a map of the earth shows that the 

 continents (or large wTinkles) conform more or less to 

 this law. But Prof. Schiaparelli' s map of Mars ^ is 

 more striking than that of the earth, when viewed by the 

 light of this theory ; but there are some objections to its 

 application to the case of Mars. If, however, there is 

 any truth in this, then it must be postulated, that after 

 the wrinkles were formed the crust attained sufficient 

 local rigidity to resist the obliteration of the wrinkles, 

 whilst the mean figure of the earth adjusted itself to the 

 ellipticity appropriate to the slackening diurnal rotation : 

 also, it must be supposed that the general direction of 

 the existing continents has lasted through geological 

 history. 



The second problem considered in this paper is con- 

 cerning the distribution of the heat, which would be 

 generated by the internal friction of the tidal distortion. 



It was shown in the preceding paper that a very large 

 amount of heat might be thus generated, and it appeared 

 at first sight as though this might serve to explain in part 

 the observed increase of underground temperature ; but 

 the solution of a certain problem concerning the cooling 

 of an infinite slab of rock 8,000 miles thick, in which heat 

 is being generated according to a certain law of distribu- 

 tion, shows that the frictional heat could not possibly 

 explain a rate of increase of underground temperature 

 near the earth's surface of more than 1° Fahr. in 2,600 

 feet. 



It follows, therefore, that Sir VV. Thomson's investiga- 

 tion of the secular cooling of the earth cannot be sensibly 

 affected by this cause. 



' Mimorie della Society degli SpetiroKo^ti lialiani, 1878, vol. vii. 



The last part of the paper does not lead to results of 

 interest to the general reader, as it is concerned with the 

 part played by inertia in the tides of viscous, fluid, and 

 elastic spheres. 



INDIAN METEOROLOGY ^ 



IN the article "Atmosphere" of the Encyclopcedia 

 Britannica it has been justly remarked that one of 

 the most important steps that could be taken towards the 

 development of the science of meteorology would be 

 extensive series of observations from such countries as 

 India, which offers splendid contrasts of climate at all 

 seasons, has a surface covered at one place with the 

 richest vegetation, and at others with vast stretches of 

 sandy deserts, and presents extensive plateaus and sharp 

 ascending peaks, all which conditions are indispensable 

 for collecting the data required for the solution of the 

 problem of atmospheric physics. In working out this 

 problem it is necessary, owing to its extreme complexity 

 and difficulty, to give attention, not merely to questions 

 immediately bearing on the physics of the atmosphere, 

 but also to climatic and other practical inquiries, which 

 may be handled with comparative ease and which afford 

 results that contribute indirectly but very materially to 

 the solution of the higher problem. The publications 

 enumerated below admirably follow up this two-fold line 

 of inquiry, and even already several important practical 

 and theoretical conclusions seem not far from the point 

 of being reached by the meteorologists of India. 



The " Report on the Meteorology of India " is the 

 second Annual Report issued since the administration of 

 the Indian Meteorological Establishment was concentrated 

 in the Central Office at Calcutta for the whole of India 

 including British Burmah and the Islands of the Bay. 

 In the scheme of publication of the monthly results 

 of the observations made at the various stations over 

 India, we note with satisfaction that the form proposed 

 by the Permanent Committee of the Meteorological Con- 

 gress at Vienna has not been adopted in some of its more 

 important details. Thus in Air. Blanford's tables, 

 instead of a general monthly mean of atmospheric pres- 

 sure, the mean monthly pressure for each hour of obser- 

 vation is given — an essential requisite for the presentation 

 of the data required in discussing various of the more 

 important problems of international meteorology. Indeed 

 these tables possess the very high merit of being, with 

 perhaps one exception, entirely suited for the discussion 

 of climatic questions of an international character — ^the 

 single exception being the lumping together of the two 

 or four daily observations of the winds into one monthly 

 mean, instead of a monthly mean for each hour of obser- 

 vation as is so admirably carried out by Professor Ruben- 

 son in his annual reports of Swedish meteorolog;^'. 



The most interesting part of this report is that which 

 deals with the failure of the rains in Western and 

 Southern India which resulted, as is only too well known, 

 in one of the most terrible and wide-spread famines of 

 recent years. The mode of treatment is grounded on the 

 practice adopted by the Office, in framing forecasts of 

 coming seasons to which we have several times drawn the 

 attention of the readers of Nature (vol. xiii. p. 66, &c.), 

 and which may be described as proceeding on the assump- 

 tion that there is a certain persistency in meteorological 

 conditions ; that, for instance, the longer a given state of 

 weather has lasted, the less the probability of a speedy 

 change ; and that as regards the distributions of pressure, 

 on which weather is so dependent, certain states of the 

 atmosphere tend to perpetuate or reproduce themselves 

 in the same region in such a manner as to maintain a 



' " Report on the Meteorology cf India in 1876." By Henry F. Blanford. 

 "The Indian Meteorolcgist's Vade-Mecuin." By Henry F. Blanford. 

 " Indian Meteorologi<^ Memoirs : " issued under the drection of Henry F. 

 Blanford. VoL i., part 2. "The Meteorolt^y of the Bombay Presi- 

 dency." By Charles Chambers, F.R.S. 



