474 Scientific Intelligence. 



that the resistance of a spark gap is so much the smaller, the 

 greater the quantity of electricity in the discharge, and that 

 within the limits of his observation the resistance of the spark 

 gap increased with the length. — Ann. der Physik, No. 5, 1904, 

 pp. 1044-1053. j. t. 



8. On the Compressibility of Solids;* by J. Y. Buchanan, 

 F.R.S. — The author has carried on a series of careful experiments 

 for the determination of the absolute linear compressibilities, 

 from pressures of 200-300 atmospheres, and at temperatures 

 between 7 and 1 1 ° Centigrade, of the metals platinum, gold, copper, 

 aluminium and magnesium. Tne method employed is that used 

 by the author in determining the compressibility of glass in 1880, 

 and developed earlier in connection with the deep-sea soundings 

 made by the Challenger Expedition in 1875. Briefly stated, this 

 method consisted in the use of a solid piezometer in which the rod 

 of the glass to be experimented upon (57 cms in length) was inserted 

 in a closely fitting tube of the same material; the two were fused 

 at one end and at the other there was an empty space of some 

 3 cms between the end of the rod and that of the tube ; a steel 

 thermometer index was inserted at the end of the rod and the 

 tube then sealed. 



"Before the instrument was attached to the sounding line, the 

 index was brought down by means of a magnet to rest on the end 

 of the internal glass wire, exactly in the same way as if it had 

 been the mercury column in a maximum and minimum thermo- 

 meter. The instrument was then sent to the bottom, or to 

 whatever depth might be decided on. During the descent the 

 temperature of the glass, both inside and outside, fell with that 

 of the water through which it passed, but as the contraction pro- 

 duced was the same on the wire and on the tube, there was no 

 differential effect to be recorded by the index. On the other 

 hand, the increasing pressure, as the instrument descended, affected 

 only the outside tube, which it shortened. In contracting, it 

 was obliged to pass the index, which was kept in its place by 

 the internal wire. When the instrument was being hove up, 

 the reverse process took place ; the tube lengthened, and lifted 

 the index clear of the internal wire by an amount equal to the 

 lengthening of that portion of the tube. As the whole clearance 

 produced by the expansion from the greatest depth did not exceed 

 lmm., its amount had to be estimated by the eye with the assis- 

 tance of a magnifying glass." 



The instrument of precision constructed in 1880 on the basis of 

 the Challenger observations was essentially the same as that 

 employed in the present research. The various parts of the latter 

 instrument were made, however, of steel. The metals experimented 

 upon were in the form of rods or wires and fitted into steel tubes 

 passing into a central steel block. The ends of the rod or wire 

 were closed with thick glass tubes kept in their places by open 



*Kead before the Koyal Society of London, Feb. 25, 1904; from an 

 advanced proof sent by the author. 



