March 22, 1894] 



NA TURE 



481 



that the measurements given below were obtained by projecting, 

 by aid of a i" objective, the image of a diamond, which was 

 rather less than 2 mm. in extreme length, into a camera, so that 

 it was enlarged upon the screen to ii cm. across. Two micro- 

 meter eye -pieces with movable wires were directed upon 

 opposite corners of the image, the diamond being manipulated 

 in the field of the object-glass till these corners were in sharp 

 focus. A movement of the wires of the reading microscopes 

 by one division of the head of the micrometer in following the 

 expansion of the image corresponded to a diametral enlarge- 

 ment of this latter by 00005 cm., but owing to imperfect 

 focus of the image no more than o"ooi could be accurately 

 determined. If the coefficient of expansion of the substance 

 were o'ooooi (that of platinum, about) the expansion of the 

 image, due to 10° C. change of temperature, is just determinable. 

 It will therefore be understood that over a wide range of tem- 

 perature considerable certainty in the readings could be secured. 

 The heating was effected by radiation from a platinum ribbon 

 folded in such a manner that the substance under observation 

 occupied the central point of a narrow platinum tube. The 

 ribbon was heated by a current. A beam of light from a very 

 small sphere — 2 mm, in diameter — of incandescent lime (heated 

 in an oxyhydrogen flame) entered the tubular oven from the 

 back. The adjustment of this beam greatly decided the sharp- 

 ness of the projected image. Temperatures were determined 



served by crystalline forces which will require to be brought 

 into play by external conditions of pressure. It is probable that 

 this is therefore an essential condition of success in its artificial 

 production. It is perhaps of little interest to add that this 

 reasoning gave rise to experiments — as I had leisure for them — 

 which I only laid aside linally upon hearing of M. Moissan's 

 success. I did not seek the aid of solution in a metal, but used 

 an apparatus to compress graphite, as well as carbon prepared 

 from sugar, between iron plates kept at a red heat, and urged 

 together by the alternate heating and cooling of the bars of an 

 iron yoke. 



I am not without hope that the use of high pressure at a high 

 temperature may ultimately prove sufficient — without resort to 

 solution in a metal — to produce diamond. If the presence of a 

 certain minute quantity of the carbide of a metal is essential, of 

 course it will fail. It is difficult to imagine, however, that it 

 should be essential. J. Joly. 



Trinity College, Dublin, March 5. 



Fig. I. 



by melting substances of known melting-points in the oven, and 

 reading the corresponding currents. Thus a curve of galvano- 

 meter readings plotted against temperature was obtained for 

 subsequent use. 



The results of the observations were four well-fixed points 

 which give a curve (Fig. l) seemingly tangential to Fizeau's 

 results at low temperatures, but which curls up rapidly at about 

 750° C. At a temperature of 850°, and indeed below this, 

 observations were stopped by the " efflorescence " upon the sur- 

 face of the diamond of flaky particles which wriggled and twisted 

 in a peculiar manner, finally disappearing. Once started, the 

 "combustion" continued till the temperature of the oven was 

 lowered to 712°. Cooling the oven, I subsequently photographed 

 one face of the diamond." The picture obtained shows the face 

 with a lamellar appearance, which was produced entirely by the 

 heating, as at starting the faces were smoothly curved. Such 

 an appearance is occasionally observed upon specimens of 

 diamond. This photograph, "as well as the curve of expansion, 

 were shown at the soiree of the Royal Society in June 1892. 

 The apparatus used was also shown in operation as applied to a 

 minute globule of a melted basalt. 



The sudden increase in volume or swelling-up of the diamond 

 at high temperatures, suggests that the diamond is a form of 

 carbon which has been subjected to high pressure when crystal- 

 lising. Such changes we may expect to be reversible, and it 

 is supposable that tquilibiium at the higher density is only pre- 



NO. 1273, VOL. 49] 



The North-East Wind. 



Prof. Bonney, in his ' ' Story of our Planet," explains the pre- 

 valence of east winds at this season as being due to the low winter 

 temperature of eastern Europe compared with the Atlantic 

 coasts. If this explanation be the 

 true one, we should expect the 

 phenomenon to occur in December 

 and January. My impression is, al- 

 though I have no accurate statistics, 

 that east winds do not prevail in those 

 months in our climate. P"urther, we 

 should expect, crossing the Atlantic in 

 winter, to find for the same reason 

 west winds prevailing off the American 

 coasts. If this is not found to be the 

 case, I would suggest the following as, 

 if not the cause, at all events one of 

 the causes, of the phenomenon in 

 question. 



The difference of temperature be- 

 "tween the northern Arctic regions and 

 the tropics, to which, combined with 

 the earth's rotation, the north-east 

 trade wind is supposed to be due, is ne- 

 cessarily greater in the spring months, 

 February to June, than on the average 

 of the year. Because in the Arctic 

 regions, little or no heat being received 

 directly from the sun between the 

 autumnal and the vernal equinox, the 

 maximum of cold should be attained 

 in March or from February to April. 

 In low latitudes these months are by 

 no means the coldest. It is reason- 

 able to expect that when this difference of temperature 

 becomes accentuated, and the gradients, so to speak, steeper, 

 the north-east winds which are due to it should become prevalent 

 in higher latitudes than those to which the trade winds proper 

 are usually confined. S. H. Burbury. 



The Suspension of Foreign Bodies from Spiders' 

 Webs. 



The following instance of the use of a stone by a spider as 

 ballast for its web is interesting. 



A web was noticed stretched between two trees at a distance 

 of about ten feet from one another. From it hung a thread 

 about two feet long, and attached to its lower end was a small 

 pebble about the size of a pea, the stone hanging free about four 

 feet from the ground. The stone had evidently been made use 

 of in this special manner by the spider for the definite purpose 

 either of keeping the web taut, or as ballast to give it stability 

 against the wind, for on lifting the stone to remove the pressure, 

 it was observed that the web became limp and slack, and was 

 stirred out of position by the least breath of air. 



This was noticed by a score or so of members of the German 

 " Turnverein " here, in the garden of whose premises the occur- 

 rence took place. R. Philipp. 



Buenos Ayres, January 24. 



