February 26, 1892.] 



SCIENCE. 



119 



tirely unknown portion of the spectrum extends about four 

 times as far from the most refrangible line hitherto photo- 

 graphed (the aluminum line 1,852), as that line is beyond 

 the blue hydrogen line of wave-length 4,861. The interest 

 in these researches is, therefore, very great; and it seems as 

 though the limit of the radiations might only be reached 

 when we can detect them in the universal ether itself, un- 

 affected by a trace of an absorptive medium, and with pho- 

 tographic plates of special chai'acter. 



The ordinary plates do not serve for work of this kind. 

 The plates used by Mr. Sohumanu are specially made by 

 himself, and are peculiar in possessing great sensitiveness to 

 the ultra violet rays, but relatively very little to the light of 

 the visible spectrum. Because of this insensitiveness to the 

 visible spectrum, the plate acts toward the ultra-violet pre- 

 cisely like one exposed to filtered light, from which all the 

 rays have been absorbed, which, as diffused light in the 

 spectrograph, would tend to cause fogginess of the picture. 

 Such is the effect when an attempt is made to photogrsph 

 the ultra-violet spectrum with an ordinary plate; for, before 

 the ultra-violet rays have affected the plate, or produced a 

 distinct image, the plate is fogged all over by the diffused 

 light. The method of making the new plates is not yet pub- 

 lished, because the investigations are not yet completed nor 

 ready for publication. 



Photography in a vacuum presents some difficulties and 

 requires far greater care than under ordinary conditions, 

 even under the most favorable conditions tlie photographic 

 effect of these extremely refrangible radiations is relatively 

 so very weak that on many plates prepared according to the 

 new method it was difHcult to establish even the existence 

 of the vibrations of the shortest wave-lengths. 



We may look forward with the greatest interest to the 

 early publication of full details and results of this most 

 skilfully conducted investigation, which has so greatly ex- 

 tended the known limits of the invisible spectrum. 



EoMYN Hitchcock. 



1455 Ma93. Ave., Washington, D.C., Feb. 20. 



METALS AT HIGH TEMPERATUEES. 



On Feb. 5, Professor Roberts-Austen, C.B., gave a very 

 interesting lecture on metals at high temperatures at the 

 Royal Institution. As was to be expected, nothing very 

 novel was brought forward, but the lecturer certainly suc- 

 ceeded in demonstrating to a large audience results which 

 have hitherto been only obtained in the laboratory. Every 

 one who has ever heard Professor Roberts-Austen lecture, 

 knows his fondness for experimenting with gold, which no 

 doubt is mainly due to his position at the mint, though, apart 

 from this, many would find a certain fascination in handling 

 and experimenting with such a metal. Moreover, gold is a 

 metal remarkable for other properties besides its monetary 

 value. On previous occasions Professor Robfrts-Austen has 

 drawn attention to the fact that its properties are changed in 

 a most remarkable manner by alloying it with small per- 

 centages of other metals, and on the present occasion he ex- 

 hibited a new series of alloys of this metal with aluminium 

 which are of equal interest to those previously known. One 

 of these alloys in particular, containing 20 per cent of alu- 

 minium, is noteworthy, as it forms an exception to the usual 

 rule that the melting point of an alloy is lower than that of 

 either of its constituents. This alloy, on the other hand, 

 has a fusing point above that of gold, the most infusible of 

 its constituents. Curiously enough, the alloy with 10 per 



cent of aluminium follows the ordinary rule. These alloys, 

 it should be added, have the most brilliant colors. The 20 

 per cent alloy is a brilliant ruby in tint, whilst those con- 

 taining greater percentages of aluminium are purpk in hue. 



With the aid of the oxy-hydrogen blowpipe and M. Le 

 Chatalier's pyrometer, the lecturer v^as able to show a large 

 audience the peculiarities of the cooling curves of several 

 metals, and also to measure the fusing points of some of the 

 most refractory of them. Indeed, he succeeded in fusing 

 iridium, using for the purpose the electric arc, the thermo- 

 couple employed as pyrometer consisting of a rod of iridium, 

 and a rod of an alloy of the same metal with 10 per cent of 

 platinum. The temperature thus reached is stated to be the 

 highest yet measured, viz., 2,000° C, and thus it is now pos- 

 sible to measure temperatures ranging from — 200° C. to 

 -f- 2,000° C, the former temperature having been attained 

 by Professor Dewar in his lecture to the Royal Institution 

 some short time back. 



Even before the invention of this instrument, Professor 

 Roberts-Austen stated that very considerable progress had 

 been made in pyrometi'y, so that Mr. Callender, with his im- 

 proved Siemens apparatus, in which the change in the re- 

 sistance of a platinum coil, as it grows hotter, is used as a 

 measure of the temperature to which it is exposed, has suc- 

 ceeded in measuring temperatures of 1,500° C, with an error 

 of not more than one-tenth of a degree. 



In measuring lower temperatures than the fusing point of 

 iridium, the thermo-couple used consisted of a couple of 

 wires, one of platinum and the other of an alloy of this 

 metal with 10 per cent of rhodium, simply twisted together. 

 This couple was inserted in the mass of a clay dish, on which 

 gold and palladium, etc., were melted by the aid of an oxy- 

 hydrogeu flame. The ends of the wires were coupled with a 

 suitable reflecting galvanometer, which by means of a power- 

 ful lantern threw a bright spot of light on a long scale fixed 

 to the wall of the lecture-room. By means of this apparatus 

 Professor Roberts-Austen was able to exhibit the recalescence 

 of iron and show that at this point the metal suddenly be- 

 comes magnetic. For this purpose a block of iron heated to 

 redness was placed on a stand fitted with a thermo-couple 

 and an ordinary magnetic needle, which carried a mirror 

 reflecting a second spot of light on the screen. At a high 

 temperature iron is non-magnetic, but as it cooled down the 

 spot of light from the pyrometer travelled down its scale, 

 till at the point of recalescence it became stationary, and at 

 the same moment the second spot of light '.-onnected with 

 the magnetic needle suddenly sveung over, showing that the 

 metal had then become magnetic. Of more immediate inter- 

 est, from a practical point of view, was a second experiment 

 exhibited. In this a bar of iron, heated to bright redness, 

 was 6xcd at one end and loaded at the other. Instead of 

 bending over under the influence of the weight, which of 

 course was not large, it remained rigid until it had cooled 

 down to its point of recalescence, when it suddenly began to 

 deflect. 



Professor Roberts-Austen maintains that these peculiarities 

 point to a re-arrangement of the molecules of the metal, and 

 that they occur even with chemically pure iron, being intrinsic 

 in the n)etal and not merely the effect of foreign constituents, 

 though of course these are of considerable importance in 

 modifying the results observed. That such changes occur 

 in practice there can be little doubt, though the effects seem 

 often to be peculiarly local. Steel plates showing very con- 

 siderable ductility on test have snapped simply from internal 

 stresses without showing the slightest signs of elongation or 



