Sep/. I 'J, 1874J 



NA TURE 



401 



It is known that when a bar of metal is lengthened by 

 means of a powerful hammer on an anvil of the same form 

 as the head of the latter, each blow produces, above and 

 below, a symmetrical contraction, the effect of which is to 

 give to the bar the aspect of a series of projections sepa- 

 rated by small level spaces. 



At the time of the collision, there spaces, which are 

 formed before and behind the impress of the hammer, 

 upon the upper and the lower face of the bar, are con- 

 nected, at a certain moment, upon the lateral faces, by 

 luminous lines passing from the one to the other, and 

 presenting altogether the appearance of an X written in 

 Hnes of tire. The phenomenon is only visible for a certain 

 temperature of bar which is being wrought, but then each 

 blow invariably produces its effect, and, in consequence of 

 the confused mingling of the imprints, we see the en- 

 tanglement of these crossed hnes which encroach upon 

 each other. These brilliant bands appear at the same 

 moment as the collision, but they do not disappear with 

 it, and their continuance was sufficiently prolonged to 

 enable us to count six luminous cross-bars visible at one 

 time, although developed by six successive blows of the 

 hammer. 



I have been able, moreover, to get this persistence 

 confirmed by several persons in the foundries of M. 

 Farcot, who, with the greatest kindness, placed his 

 services at the disposal of the Metric Commission for the 

 execution of the work. 



Although the lines of the cross-bars appeared to us all 

 rectilinear, and although we could not compare them to 

 anything better than two series of straight lines, parallel 

 and intercrossed, we think it will be indispensable to 

 determine their form more exactly by appropriate pro- 

 cessts, and to discuss it with the greatest care. 



It is well known that hammerin;^ develops heat in the 

 bodies hammered ; thermodynamics teaches us that these 

 thermal effects ought to be regarded as the result of 

 mechanical work or of dtini-forcc vive exerted during 

 the collision, but the precise place in which the calorific 

 development is produced has not yet been noticed. 



For ourselves, we do not hesitate to affirm that the 

 zone which becomes luminous is that along which the 

 matter mainly flows, at the moment when the change 

 of form takes place, according to a law which we were 

 enabled to discover in our previous researches in mole- 

 cular displacements. If this first indication should be 

 confirmed, there would be thus obtained a more exact 

 knowledge of the mode of distortion determined by the 

 forging, and the phenomenon which we describe would 

 evidently form a new scientific connection between ther- 

 modynamics and the question with which we ourselves 

 are personally occupied under the title of " Flowing of 

 Solid Bodies." 



The phenomenon ought to be the same for all metals, 

 and we have already ventured to hazard some considera- 

 tions of the particular causes of the brightness which it 

 presented in the case of platinum, and which has not, so 

 far as wc know, been yet observed in any other forging. 



The exceptional hardness of the platino-iridium, cooled 

 to a dull red heat, requires, for an equal distortion, an 

 amount of work at least equivalent to that of the forging of 

 steel, and in consequence of the relative smallness of the 

 calorific capacity of this alloy, this same work ought to be 

 converted into calorific phenomena, more localised and 

 more intense. Moreover, the material is more homogeneous 

 than iron, and is notable lor a kind of remarkable trans- 

 lucency which makes one believe that the eye can follow 

 the shade of red to a certain depth. The effects, whatever 

 they may be, are thus rendered more manifest, more espe- 

 cially as they are not accompanied by any exudation of 

 foreign matter nor by any oxidation of the surlace. All 

 these circumstances are eminently favourable to the ob- 

 servation which chance permitted us to make, and which, 

 once confirmed in the case of platinum, may certainly be 



renewed with other metals, although possibly in a more 

 restricted manner than in the case of the alloy of MM. 

 Deville and Debray. 



We confine ourselves for the present to a summary indi- 

 cation of the principal fact, which appears to us to have a 

 certain importance, and which consists in this appearance 

 of luminous bands which arise from collision, and the 

 position of which enables us to fix the precise place where 

 is developed the heat which represents under another 

 form the work done by motion ; this fact is, perhaps, of a 

 nature to open some new path for the researches, so care- 

 fully made, of the physicists of our epoch on all that touches 

 on molecular mechanics and on the calorific actions which 

 are connected with them. 



The ingot of platinum has already been brought into 

 the form of a bar with a square section of 4*50 m. in length ; 

 there will be a chance of continuing the same observa- 

 tions in the new operations of forging to which it will be 

 submitted ; the chance of renewing them may perhaps 

 not again be offered. 



SUBJECTS FOR PRIZES PROPOSED B Y THE 

 HAARLEM SOCIETY OF SCIENCES 



'T'HF, following subjects for prizes are proposed by the Haarlem 

 Society of Sciences : — 

 I. Competition of 1S75, 'he limit of which is fixed on 

 Jan. 1, 1S75. 



1 . To give for ten sorts of glass of known chemical composition — 

 (a) The coefiScients of dilatation between o°and (at the most) 100°, 

 having regard to the influence of the tempering and the state ijf 

 tension; (/') The coefficients of elasticity with exact indication of 

 the temperatures ; (c) The indices of refraction for at least tf n 

 points distributed over the whole extent of the spectrum, al^o 

 with precise indication ol the temperature. 



2. Does the coefficient of dilatation of steel vary with the 

 degree of tempering, and can we establish empirical laws on the 

 subject of the connection between these two elements ? 



3. Can there be established by experiment a connection 

 between the diffusion of liquids through porous partitions and 

 other phenomena, such as capillarity, &:c. ? 



4. Determine the coeflicieut of dilatation for at least three 

 liquids of simple composition, according to the process hy which 

 the absolute dilatation of mercury has been established. 



5. Researches are souglit on the origin of sensitive organs, 

 especially of the visual organ, among some of the inferior 

 animals ; this origin being considered, as far as possible, in 

 relation to the conditicms in which the animal is found, and the 

 external influences to which it is subject. 



6. In terrestrial magnetism, what are the periods known with 

 sufficient accuracy, and how far have these periods been proved 

 to be connected with cosmicil or telluric phenomena ? 



7. New experiments and observations are wanted to clear up 

 the following question : — Mow are albumenoid matters formed 

 and removed in plants ? 



S. Determine exactly the density, the coeflicient of dilatation, 

 the point of fusion, the point of ebullition, the specific heat, the 

 index of refraction, and the specific rotatory power of at least 

 twenty organic combinations, pairs of which are isomeric and 

 whose chemical composition is known. 



9. The experiments of M. Regnault on the specific heat of 

 certain terpenes, and those of M. Berthelot on diamylene and 

 triamylene, having shown that the specific heat of polymeric 

 bodies of one combination may be equal to that of the funda- 

 mental matter from which they originate, it is desired that these 

 researches be extended to as great a number as possible of other 

 combhiations having between them tlie same relations, for the 

 purpose of deciding if the observed fact may or may not be 

 raised to the rank ot a general law. 



10. New researches .are sought on tetraphenol and its deriva- 

 tives, for the purpose of deciding on the value of the hypothesis 

 of M. Limpricht concerning the existence of a series of aromatic 

 matters with a nucleus composed of four atoms of carbon. 



11. Give a critical sketch of experiments and observations con- 

 cerning the existence of Baclcyia in contagious diseases, followed 

 by original researches on the same question investigated in one 

 or more of these maladies. 



