248 



NA TURE 



[January ii, ic,co 



will be amply rewarded by the discovery of many new forms, 

 whatever group he may choose to take in hand. Mr. P. 

 Marshall recently described sixty-six species in a first instalment 

 of New Zealand diptera, fifty-four of which were new {Trans. 

 N.Z. Inst., vol. xxviii.). 



As the general laws regarding the distribution of species can 

 only be discovered from the knowledge of a very great number 

 of facts, I fully agree with the Rev. T. Blackburn that " the 

 special task to be accomplished by this generation, and in the 

 present state of knowledge, is that of collecting and recording 

 facts and data'" (Presidential Address, Trans. Roy. Soc. South 

 Australia, 1891, vol. xiv. p. 371) ; and that when we attempt 

 to generalise we find how very little is known in comparison to 

 what is yet to be discovered, and feel "the need of that ex- 

 haustive collection of the data and records of the facts that we 

 are at present engaged in procuring." Nevertheless, I cannot 

 concur in the suggestion that we should altogether relegate 

 " the investigation of the reasons of the facts of nature " to the 

 naturalists of the next generation. Not only is it even now 

 exceedingly interesting and important to summarise what we do 

 know and to understand the direction in which our observations 

 are tending, but it also makes all future work immensely more 

 interesting, and enables the work to be carried out more in- 

 telligently and thoroughly. It is, however, very necessary when 

 recording facts to have the mind free from all theories and 

 preconceived ideas which might in any way influence one's 

 observations and conclusions. H. Farquhak. 



Wellington, N.Z. 



The Resistance of the Air. 



Referring to Mr. Bryan's summary, on page 107 of the 

 current volume of Nature, of the observations on the resistance 

 of the air, made by Le Dantec and by Canovetti, it is but fair 

 to say that the conclusion "No. 3," viz. that the resistance to 

 a plane surface depends upon its contour, i.e. whether circular, 

 square or triangular, is by no means new. Precisely this result 

 was deduced by Prof. Hagen, of Berlin, in his most delicate 

 experiments published by the Berlin Academy in 1874. His 

 memoir is the first in Abbe's collection of translations, entitled 

 " The Mechanics of the Earth's Atmosphere," and a detailed 

 discussion of his results is given at pp. 234-238 of his " Treatise 

 on Meteorological Apparatus and Methods." Hagen's results, 

 when expressed in grams, decimetres and seconds, give the 

 resistance per square decimetre as (0-00707 + 00001125/) z^- 

 where/ is the contour of the plate and v the velocity. As his 

 experiments were made with plates of only from i to 12 deci- 

 metres on a side, and as he showed that the size affects the 

 coefficient quite as much as the shape, it would scarcely be 

 proper to exterpolate from his small plates up to the large ones 

 used by the French investigators. We should not expect any 

 close agreement for a surface of one metre square between 

 Hagen's figures and these newer ones, but the general law that 

 the pressure per square unit depends upon both the size and the 

 shape of the plate is due to Hagen. The explanation of this 

 result is also largely due to him ; it is not merely a question of 

 gaseous viscosity or internal friction, but especially of that dis- 

 sipation of energy that occurs in the ideal perfect fluid, and 

 which has been called convective friction in the above-mentioned 

 treatise and elsewhere. Le Dantec and Canovetti, by experi- 

 menting on a large scale, have necessarily encountered such 

 irregularities and difficulties as must have limited the accuracy 

 of their results quite as much as in the case of many other 

 experiments since those of Sir Isaac Newton. In general, 

 inasmuch as resistance per square unit varies with the size and 

 shape of plane plates or other bodies, it can hardly be called an 

 important physical constant of great scientific interest. It 

 certainly has a practical interest to the aeronaut, the navigator, 

 and the millwright, but the scientific interest of such experi- 

 ments consist essentially in determining the lines of flow and 

 the transformations of energy involved in the discontinuous 

 motions. C. A. 



Washington, December 13, 1899. 



The object of my notice was to give a general account of Le 

 Dantec's and Canovetti's experiments, and certainly not to 

 deliver judgment on those delicate questions of priority which 

 are mainly of personal interest. The "law of perimeters" 



NO. 1576, VOL. 61] 



being so noticeably put forward as a new result, I could do 

 no less than cite the views of Le Dantec and his referee, be- 

 tween whom and Hagen or his advocate " C. A." the matter 

 must rest. There is surely a contradiction of terms in your 

 correspondent's expression, " that dissipation of energy that 

 occurs in the ideal perfect fluid, and which has been called 

 convective friction in the above-mentioned treatise and else- 

 where." A fluid which dissipates energy, especially by means 

 of anything called friction, is not an "ideal perfect fluid" accord- 

 ing to universally accepted definitions. As to the "scientific 

 interest "of determinations, not only of the aerial resistance of a 

 square metre, but also of the weight of a cubic centimetre of 

 water, the so-called mechanical equivalent of heat, the electrical 

 resistance of a copper wire, the E.M.F. of a Clark cell, or any 

 other physical quantity whose value is aff"ected by various con- 

 ditions, this surely is a matter of opinion ; but the great amount 

 of attention which is now devoted to accumulating statistical 

 data of this class is sufficient indication of a general consensus 

 of opinion in favour of such researches being regarded as valu- 

 able from a scientific standpoint. G. H. Bryan. 



Grey's Rock Paintings. 



In Prof. Haddon's review of Mr. Mathews' " Eaglehawk 

 and Crow " there are several references to Cirey's rock paintings, 

 amongst which your reviewer remarks, " These rock paintings 

 are certainly very puzzling, and deserve renewed investigation 

 on the spot." They were investigated by Mr. A. C. Gregory, 

 the Australian explorer, who, about seventeen years ago, gave 

 me the following particulars relating to them : — 



"The importance of the native coloured drawings, published 

 by Grey in his " Travels," is much exaggerated. The colovirs are 

 by no means so bright as printed, and the drawings are generally 

 of a very primitive kind, more or less crude outlines of hands 

 or weapons placed on the face of rocks, and lines marked round 

 the edge of the object" (sec Jour. Anth. Inst., xvi., p. 133). 

 I have also a clear remembrance of Mr. Gregory blaming the 

 printers for attempting to make comparatively finished drawings 

 of the faces out of crude outlines much in the same way as was 

 so commonly done in the elaborate plates that accompany the 

 volumes of Cook's "Voyages." Mr. Mathews' "identification" 

 may therefore be dismissed. H. Ling Roth. 



Halifax, Yorks., January i. 



Evidence of Upheaval in Vanua Levu, Fiji. 



During an examination of the geology of this large island 

 evidence of very extensive upheaval frequently came under my 

 observation. Speaking generally, the main elevated mass of the 

 island is the product of submarine fissure-eruptions. Its surface 

 is in great part traversed by mountainous ridges, which form an 

 intricate system, and consist in each case of an axis of basic 

 and often coarsely crystalline volcanic rocks concealed beneath 

 calcareous tuffs and volcanic muds, which in their turn are 

 covered over by agglomerates. During the movement of up- 

 heaval, and in the ages that have since elapsed, the denuding 

 agencies have been so actively at work that it is not easy to 

 restore the original form of the surface ; but it may be observed 

 that in the eighteen months of my stay no evidence of a crateral 

 cavity came under my notice in the main mass of the island. 

 By studying the contours it can be shown that \'anua Levu has 

 been formed by the union during the process of upheaval of a 

 number of smaller islands with a central larger island. 



Foraminiferous and pleropod- bearing muds together with 

 calcareous volcanic tuffs are not infrequent up to elevations of 

 iioo or 1200 feet. They are of scanty occurrence at greater 

 heights ; but they are to be found in diff"erent parts of the island 

 at elevations of from 1500 to 2000 feet ; and in one locality I 

 found sea-shells in a coarse tuff at 2200 feet. Elevated coral- 

 reefs have taken a very little part in the building-up of the 

 island. They exist in a few localities at the coast, and do not 

 attain a higher level than some 200 feet. In this connection it 

 should be noted that flints and silicified corals occur on the 

 surface of the lower regions all over the island. Corals in 

 various stages of silicification are found in quantities in some 

 places, especially where a low-lying district now marks the 

 situation of what was once an inland sea. H. B. GuPPY. 



R. C. Mission, Rewa, Fiji, November 21, 1899. 



