Ai'Rii. 20, 1905] 



NA rURE 



58: 



The late Prof. Tacchini. 



As a tribute to the memory of the late distinguished 

 Italian astronomer, of whom an obituary notice appeared 

 in the columns of Nature last week, may I be permitted 

 to add a few personal reminiscences? Prof. Tacchini took 

 part in the eclipse expedition of 1875 to the Nicobar 

 Islands. He joined our party from India, where he had 

 been staying from the previous year, having been com- 

 missioned by his Government to make observations on the 

 transit of Venus of 1874. The Italian Government sanc- 

 tioned his remaining in India until the following year in 

 order that he might make use of the opportunity with the 

 instruments in his charge for the observation of the forth- 

 coming total solar eclipse. Of the little band of observers 

 who assembled on the Island of Camorta in April, 1S75, 

 most are happily . still with us. Vogel, the introducer of 

 " orthochromatic " photography, has passed away, but 

 Pedler, Waterhouse, and others will remember the pleasant 

 camaraderie which existed between ourselves and our 

 Italian colleague. The expedition failed in its object 

 through a cloudy sky, and we were all more or less the 

 victims of intermittent malarial fever : but we made the 

 best of adverse circumstances, and under conditions which, 

 to many a party of observers similarly placed, would have 

 been extremely trying, the good understanding which the 

 members had arrived at among themselves helped to lighten 

 the burden of our disappointment. Not the least weighty 

 factor in the formation of this good fellowship among the 

 representatives of different nations was the geniality of 

 Tacchini, with whom we parted on the P. and O. steamer 

 Baroda on the homeward voyage with every regret. 



.'\pril 15. R. Meldol.a. 



Propagation of Earthquake Waves. 



Mr. Rudzki, in his letter to Natl'rf. of April 6, observes 

 that " it is only for perfectly elastic and isotropic bodies 

 that the separation of the dilatational (normal) from the 

 tortional (transverse) wave takes place with certainty " ; 

 and his conclusion is that " it is more than highly im- 

 probable that the effect of internal friction would neutralise 

 the effect of Eeolotropism. " If the term " internal fric- 

 tion " is intended to refer to the effect of pressure, this 

 objection was forestalled by Major Dutton by the remark 

 that " towards this more compact and continuous con- 

 dition (of a compact mineral substance with a feeble pro- 

 nounced cleavage), the pressure of great depths in the 

 earth should, it may seem, tend to bring the material 

 subject to it." 



To me it is refreshing to learn that any objection can 

 be raised to the view that the two speeds of earthquake 

 waves are respectively condensational and tortional, the 

 latter being held to prove a high degree of rigidity for 

 the interior of the earth. 



To examine the question whether the interior is to a 

 considerable depth liquid or solid formed one subject of 

 my "Physics of the Earth's Crust," and I came to the 

 conclusion that it is liquid ; and, so far as I am aware, 

 my arguments have never been refuted. On this question 

 Sir A. Geikie writes (N.-iture, February 9), " the geo- 

 logical belief rests upon a large body of evidence from 

 the structure of the terrestrial crust, which it is difficult 

 or impossible to explain except on the supposition of an 

 internal mass which, at least in its outer parts, is suffici- 

 ently liquid to emerge at the surface as molten lava." 



To produce arguments on the opposite side of the ques- 

 tion is another matter, and that derived from the two 

 speeds of earthquake propagation is perhaps the strongest. 

 I was consequently led to inquire whether the same result 

 could not be obtained on the hypothesis of a liquid magma 

 holding water gas in solution, subject to Henry's law 

 that the same volume of gas can be absorbed by a given 

 volume of the liquid at all pressures. The result which I 

 obtained was that two waves would be propagated with 

 different velocities, the one a condensational wave depend- 

 ing on the elasticity of the liquid, and the other a wave 

 depending upon the pressure and the volume of the gas 

 which could be held in solution bv a given volimie of the 

 liquid. 



If e be the elasticity of the liquid and D its density, 



NO. 1851, VOL. 71] 



then s'e/D will be the velocity of the condensational wave. 

 .'Vnd if P be the pressure and rV the volume of gas which 

 can be held in solution by the volume V of the liquid, 

 then v'P/rD will be the velocity of the gaseous wave. 

 If we accept Laplace's law of density, P/D will increase 

 with the depth, and r will probably decrease, hence the 

 velocity of the gaseous wave will increase {Proc. Cam- 

 bridge Phil Soc, vol. xii., part v., 1903). 



Harlton, Cambridge, April 10. O. Fisher. 



The Ancient Races of the Thebaid. 



On my return to Oxford 1 saw Prof. Pearson's letter in 

 vour issuo of March 30. 



Since Prof. Pearson admits that he is not an anatomist, 

 it w^ould serve no useful purpose to discuss with him the 

 anatomical value of the criteria which Mr. Maclver and 

 I employed in our analysis of the skulls of the ancient 

 inhabitants of the Theban province of Eevpt. 



The letter may be regarded as an interesting record of 

 a method of interpreting percentage values adopted by a 

 professed statistician. Arthur Thomson. 



Oxford, April S. 



There is an old saying that all good science is short- 

 hand common sense. I am sorry that Prof. Arthur Thom- 

 son does not think it worth his while in the case of his just 

 published far-reaching negroid cranial criterion to con- 

 vert the esoteric methods of the anatomist into simple 

 language for the benefit of other readers of Nature, if 

 not for that of the "professed statistician." I hope he 

 will meet me later when I ask him to discuss, as I propose 

 shortly to do, the mathematico-statistical treatment of his 

 volume, which is of a somewhat remarkable character. 

 Meanwhile, in order to expedite those further investigations 

 bv professed craniologists which his discovery is exciting, 

 it w^ould be of great value if he would tell us to what 

 negro series he, o priori, applied his criteria, and what 

 percentages of pure negroid, non-negroid, and intermediate 

 crania he found in that series. Karl Pearson. 



Inversions of Temperature on Ben Nevis. 



The recent letters of Mr. Dines and Mr. Rotch (N.ature, 

 February 16 and March 30) have suggested that a note 

 as to the occurrence of temperature inversions on Ben 

 Nevis may be of interest. 



During the thirteen years 1891-1903, occasions were not 

 infrequent when the temperature at the top of the moun- 

 tain (4406 feet) was higher than that at the base. These 

 inversions have been grouped according as the summit 

 temperature was the higher, (i) at one hour at least of 

 the day ; (2) at each of the twenty-four hours of the day ; 

 (3) on the mean of the twenty-four hours of the day. 



The total number of cases in the thirteen years was as 



follows: — 



Clas. 1. Class U. Class III. 



January 7 •■• — ••• 3 



February 18 ... i ■■. 5 



March ' n .•■ — •■■ ' 



April q ■■• — ■•• — 



May 7 ••■ — - — 



June 8 ... — ... 



July 4 - — - — 



.\ugust 4 ■•• — ■•• — 



September ^^ ••• — ■•• 3 



October 15 •■• — ■■■ S 



November 29 ... 3 .•■ 8 



December 24 ... 5 ... 8 



Year 158 9 33 



Thus inversions occurred at all seasons, but inversions 

 continued throughout the twenty-four hours of the civil 

 day only in February, November, and December, and those 

 of Class III. only between September and March. The 

 average difference of temperature between Ben Nevis and 

 Fort William ranged from i6''-8 F. in April to i4°-4 in 

 December, the mean for the whole year being i5°-4. Hence 

 inversions were at all seasons large departures from the 

 usual conditions. 



