August 2, 1895.] 



SCIENCE. 



129 



rather was that the cerebral capacity does 

 not necessarily prove that the person who 

 carried the skull was of extremely low stat- 

 ure. In fact, up to the present time, though 

 individual dwarfs are known to have ex- 

 isted in America, and are even said to have 

 been artificially cultivated in Mexico for 

 the amusements of the nobles (!), no dwarf 

 tribe has yet been discovered. 



AMERICAN OBJECTS IN NEPHRITE. 



The proceedings of the Berlin Anthro- 

 pological Society for January last contain a 

 description by the well known archseolo- 

 gist. Dr. A. Ernst, of Caraccas, Venezuela, 

 of three nephrite axes from that region, one 

 of them found by himself. All three are of 

 rather clear, green color, not presenting the 

 milkiness of the so-called Chinese article — 

 A trait which characterizes the specimen 

 from the same locality which has long been 

 in the Museum of Berlin, and which partic- 

 ularly attracted the attention of the late 

 Dr. Heinrich Fischer, and which he dwells 

 on as important in his classical work, 

 ' Nephrit und Jadeit ' (pp. 7, 347). 



It is true that up to date we do not know 

 the deposit from which these South Ameri- 

 can species were taken, but it seems a long- 

 way to go to look for it in Burmah or Tur- 

 kestan, as some would advise. Mineralo- 

 gists are now of the opinion that neither 

 thb coloring nor the chemical composition 

 of these allied minerals is sulficient to desig- 

 nate their source. A better criterion is 

 their microscopic structure. This presents 

 marked and peculiar differences, and if the 

 American specimens could not be traced to 

 any known site on this continent, and pre- 

 sented all the lithological traits of the 

 Asiatic article (which they do not, in as 

 far as examination has proceeded), then 

 there would be some basis for such specu- 

 lations. 



D. G. Brinton. 

 TJniveesity of Pennsylvania. 



PHYSICS. 



LORD KELVIN AND MR. MURRAY ' ON THE 

 TEMPERATURE VARIATION OF THE THER- 

 MAL CONDUCTIVITY' OF ROCKS.'* 



In the recent interesting revival of the 

 question of the probable ' Age of the Earth ' 

 it has developed that it would be verj^ con- 

 venient if it were known whether rocks con- 

 duct heat more readily when hot than when 

 cold. Not much was known on this point, 

 and the research bearing the above title was 

 carried out with a view to determining 

 whether conductivity varied with tempera- 

 ture, and if so whether directly or indirectly. 

 In a general way, the plan of the experi- 

 ment was to produce a steady flux of heat 

 between the two ends of a column of the 

 rock under examination, the temperature of 

 these ends being kept constant, and then to 

 measure the temperature at three points 

 within the column arranged in a line coin- 

 cident with the flux line. The ratio of the 

 mean conductivities for the portions of the 

 rock between the first and second points 

 and the second and third would then be de- 

 fined by Fourier's theoiy of conductivity, 

 as a function of the steady temperature at 

 these points and the distance between them. 



The columns of rock were not large, be- 

 ing generally about three or four centi- 

 metres square and six or eight centimeti'es 

 high, although somewhat larger in one or 

 two cases. They were si)lit in halves in a 

 vertical plane parallel to the flux line, to 

 allow of the introduction along the centre 

 line of thermo-electric junctions consisting 

 of platinoid and copper. These were of 

 wire fitted in small grooves, and the two 

 parts were then pressed tightly together so 

 as to resemble an unbroken column as nearly 

 as possible. The lower end was kept at a 

 nearly constant high temperature by means 

 of a bath of molten tin. The upper surface 

 was covered with mercury into which the 



* A paper read before the Royal Society on May 30. 



