202 



NATURE 



\yan. lo, 1878 



quick in their movaments, which increased the difficulty of 

 observation, but that the bees themselves were the agents, in 

 making the holes, there can be no reason to doubt. 

 Highfield, Gainsborough, December 21 F. M. Burton 



Photography Foreshadowed 



The firat prophetic allusion to the photographic art, the dis- 

 covery of which was to take place eighteen centuries later, is 

 perhaps found in the story of the miraculous occurrence told in 

 the life of St. Veronica. 



The second instance is about the year 1690; but intermediate 

 instances may probably be found. 1 extract from the works of 

 Fenelon ^ the loUowing passage from an imaginary voyage in 

 1690 : — " There was no painter in the country, but when any- 

 one wished to have the portrait of a friend, a beautiful landscape, 

 or a tableau which represented any other object, he put water in 

 large basins of gold or silver ; then placed this water opposite 

 the object he wished to paint. Soon the water congealing 

 became like a looking-glass, in which the image of that object 

 remained ineffaceable ; and it was a picture as faithful as the 

 brightest mirrors." One could wish that the author had entered 

 into detail as to the manner " of placing this water opposite the 

 objects he wished to paint." 



The third instance is about 1760, that is seventy years later, 

 and seventy-nine years before 1839, the date of Daguerre's dis- 

 covery. It is reported ^ by Ed. Fournier, who extracted from 

 what he calls "un assez mauvais livre," written by a certain 

 Tiphaigne de la Roche '^, the entire passage, extremely curious, 

 but rather long. This passage contains many details. The 

 " water " of Fenelon is replaced by "a material very subtle, 

 very viscous, and very ready to dry and harden." "They" 

 (certain "elementary spirits") coat with this material a piece of 

 linen, and present it lo the objects which they wish to paint," &c. 



In the two last examp es the pictures formed reproduce the 

 images of the objects, with their natural colours and their forms, 

 so that the objects are seen as if reflected in a mirror. The 

 photographs of the present day are still very far from this ideal 

 perfection, which, however, they will probably never cease to 

 approach without ever being able to reach. 

 • Rotterdam J. A. Groshans 



Average Annual Temperature at Earth's ^Surface 

 Having lived for many years both in the southern and 

 northern hemispheres, I have a very strong impression that if 

 means were taken to ascertain, with more or less approximation, 

 the average annual temperature at the earth's surface, by a com- 

 bination of the daily averages of a sufficient number of places of 

 observation, there would be found a very considerable differ- 

 ence in the yearly values of the said average annual temperatures. 

 But whether, on inquiry, there should prove to be a decided 

 difference or an absolute agreement between these averages, the 

 fact in either case would surely be worth ascertaining, and could 

 not fail to be instructive. It might be objected that it would be 

 impossible to obtain the observations of the daily average tem- 

 perature from such a number of observatories as would render the 

 desired annual average for the whole earth of nny value, but I 

 think this objection overstates the difficulty. Suppose that the 

 subject were taken up by some one of the meteorological autho- 

 rities in Great Britain, it would not be difficult to obtain from 

 existing daily records, a good average annual value for the tem- 

 perature of the British Islands. Similarly, an average annual 

 value could be obtained for the temperature, from the daily 

 averages in the various colonies and dependencies of the British 

 impire; and I take it to be certain, that the conductors of the 

 various meteorological observatories all over the empire would 

 cheerfully respond to an invitation to co-operate in such a work. 

 In a similar scientific spirit it is to be hoped that the observatories 

 of all civilised countries would be willing to exchange their 

 observations, and an approximate result could thus be arrived at, 

 possibly in two or three years. Certainly, it might be at first a 

 rough approximation only, but it would be yearly becoming better 

 with the rapid increase ot meteorological observatories all over 

 the world. And as it is not too much to hope that, sooner or 

 later, the whole habitable earth will be civilised and covered with 

 observatories, it is certain that the figures ultimately obtained to 

 represent the average annual temperatures at the earth's surface 



» Paris, Auguste Desrez, 1837, tome 2™*, p. 643. 



* Le VieuxNeuf, Hiitoire Ancienne des Inventions et D^couvertes 

 Modernes Paris, Dentu, 1859. 

 3 Giphantie, a Baby lone, MDCCLX., 12°. 



would have the value of scientific approximations of considerable 

 accuracy. If this be so, it cannot be too early to begin these 

 statistics now. 



Supposing that these annual averages should exhibit a differ- 

 ence in their yearly values, it is pirobable that these differences 

 would vary in sympathy with the total sun-spot areas of the years 

 to which they belonged. What could be done for temperature, 

 could be done at the same timfe for othef subjects of meteorological 

 investigation, and it is impossible to anticipate at present what 

 light these tabulated annual averages might be able to throw 

 upon various problems of solar and terrestrial physics. 



Balham, December 4 D. Traill 



ON A MEANS FOR CONVERTING THE HEAT- 

 MOTION POSSESSED BY MATTER AT 

 NORMAL TEMPERATURE INTO WORK 



IN a previous article ^ we cons5dered how, by a simple 

 mechanical means, dififusion renders it possible to 

 derive work from matter at normal temperature. As the 

 subject is an important one we propose to develop it 

 somewhat further here. ' 



2. The normal temperature of objects on the earth's 

 surface represents a vast store of energy in the form of 

 molecular motion. The sea (for example) at normal tem- 

 perature possesses an amount of molecular energy which 

 (by computation), if it wtre entirely utilised, would be 

 competent to lift it to a height of upwards of seventy 

 miles. The air and the crust of, the earth itself possess 

 comparable amounts of energy. It might therefore well 

 be asked beforehand whether it is not possible to transfer 

 some of this intense molecular motion to masses and 

 utilise it. It may be observed that this intense store of 

 energy is being continually dissipated in space in the form 

 of waves (by radiation). The energy possessed by the 

 molecules of matter, however, maintains (as is known) a 

 constant normal value on account of the waves of heat 

 received from the sun, whose mechanical value at the 

 earth's surface (as represented by the results of Herschel 

 and Pouillet) is normally equal to about one-horse power 

 per square yard of surface. Here, therefore, we have a 

 continual store of motion kept up in the molecules of 

 matter on the earth's surface to be wasted in great part in 

 imparting motion to the ether of space. It would cer- 

 tainly look, d, priori, as if there ought to be some means 

 of utilising this store of motion. 



3. The second law of thermodynamics would (as is 

 known) assume that this would not be practicable. This 

 law was propounded simply as what was considered a 

 legitimate inference from the observed behaviour of heat. 

 But a great advance in the knowledge of the nature of 

 heat has been made since that time, and it should be 

 noticed that the law is (admittedly) by no mcaps theo- 

 retically necessary or requisite to satisfy the principle of 

 the conservation of energy. Indeed a conceivable case 

 opposed to it has been pointed out by Prof. Maxwell, 

 though one not capable of being practically carried out. 

 It was my purpose in the last article to direct attention to 

 a physical process opposed to the law and admitting of 

 practical realisation,'^^ in the effects attendant on the dif- 

 fusion of matter. At' the time when this law was enun- 

 ciated the character of the motion termed "heat" (as 

 illustrated in the now accepted kinetic theory of gases) 

 was unrecognised, and therefore the mechanism of the 

 diffusion of gases was not understood. Under these 

 conditions, therefore, it would not be much a point for 

 surprise if increase of knowledge should show the law 

 not to be generally applicable (or not to admit of that 

 general application which is implied by the use of the 

 term " law "). 1 { 



4. It may serve greatly to facilitate the following of this 

 subject if we visualise the relations of heat and work 

 more closely. Since " heaf^ is simply a motion of small 

 portions of matter (termed " molecules "), and sirice the 



I '■ On the Diffusion of Matter in Relation to tke Second Law of Thermo- 

 dynamics, " see Nature, vol. xvii. p. 31. 



