Oct. 1 1, 1877] 



NATURE 



501 



the one to the other is unintelligible There are many dilti- 

 culties connected with the subject of potential energy which the 

 progress of science is likely to remove, but they are not to be got 

 over by the verbal alteration proposed by your correspondent. 

 The enert:y of compressed air was at one time supposed to be 

 potemiil and is now regarded as kinetic. Further inquiries into 

 the constitution of matter may enable us to see that many forms 

 of energy which are still regarded as potential are really "actual." 

 Meanwhile we may, I think, suppose potential energy to mean the 

 power of acquiring the power of doing work and to be located 

 in the system possessing ihis power. P. M. 



The Arts Club, October 7 



Indications of the Ice-age in Shetland 

 Shetland will now be narrowly searched for proofs of 

 glacial aciion by every tourist who takes an interest in such 

 vestiges of a bygone era. Smoothed surfaces, strias, and grooves 

 are so abundant and distinct on Mr Peach's ground — the sand- 

 stones on the shores of the Loch of Ciickhemin, and of the im- 

 mediately adjoining bay — as to have long ago suggested the 

 innocent or waggish notion that the la't were scratches made by 

 the p:ows of the Norsemen! Still on the mainland, but some 

 forty miles distant, on the shores of the magnificer.t bay of St. 

 Magnus, stri.-e are to be seen on the sandstones ot the haaf- 

 fishing station at Stennis, and till, or boulder-clay, lies in patches 

 on the Tuans ol Hillswick. Ice has ma'ie distinct markings, 

 running east and west on the gneissose rock close by the door of 

 the tarm-house of Ailesbargh, which is perhaps about a mile 

 north of the narrow isthmus of Mavis-Grind. The huge mo- 

 raine-looking mound, which lies between the south -nst foot uf 

 Ronas-hill and the head of Ronas-voe, claims a special xamina- 

 tion by those who wish to be further satisfied as to tlie former 

 existence, or otherwise, of glacial action in Shetland. G. G. 



The Discoverer of Photography 

 In your account of the death of Mr. Fox Talbot (Nature, 

 vol. xvi. p. 464), you state that he first entertained the idea of 

 the art of what is now called phoiography in 1833, and that it 

 was rot till 1839 that he and Daguerre first made known the 

 principles of photography under the name, I think, first of 

 Daguerrotype, followed by Talbotype. I therefore think the 

 following notes concerning Niepce may interest some of your 

 readers : — 



I cannot now from memory give exact dates, but I think it 

 was at least ten years previous to 1839 that there lodged in a 

 neighbouring house to where I now reside a Frenchman of the 

 name of Niepce ; he was, I think, engaged on a perpetual motion 

 machine..' He died, which necessitated his brother coming from 

 Paris to Kew. The brother was a theatre scene- painter, and had 

 discovered the art of fixing upon metal the pictures of objects re- 

 flected by the sun. On arriving at Kew he put up at the " Coach 

 and Horses" Inn, then kept by Mr. Cusel, and not being able to 

 speak English, Mr. Cusel introduced him to Mr. Francis Bauer, 

 the celebrated botanical artis', then residing at Kew. Niepce 

 had brought with him three pictures, specimens of his discovery, 

 which he showed to Mr. Bauer, who became much interes:ed in 

 them. He deemed the discovery worthy of being made 

 known to the Royal Society, but as the method of obtaining 

 the pictures was not described in the notice sent to the 

 Society, they would not entertain it, and nothing was done 

 in the matter. Niepce returned to Paris, leaving two of 

 the pict'jres with Mr. Bauer, and the third with Mr. Cusel 

 in part payment of his bill, he being a poor man. Being a fre- 

 quent visitor to Mr. Bauer, the latter naturally called my attention 

 to the two pictures that hung in his room for at least ten years. 

 In time Niepce let the secret of his discovery become known to 

 M. Daguerre, and in 1839 this discovery came before the public 

 under ttie name of " Daguerreotype," and about the same time 

 " Talbotype " was announced. This led Mr. Bauer to write a 

 letter to the Athciucum, fully explaining all particulars of what 

 I have here stated from memory. In his letter Mr. Bauer said 

 he should be happy to show the pictures to those interested in 

 the subject. Consequently he had many callers, one of the 

 earliest being Dr. Percy, whom I remember coming to me, want- 

 ing to know where he could find Mr. Cusel, who had then retired 

 and was living at Richmond. Dr. Percy went off to Richmond 

 with the intention of buying the picture, but I remember telling 



him Mr. Cusel would not sell it as he was not in need of money. 

 Such was the case, as Mr. Cusel told me some time after " that 

 he would not sell it ; no ! not if he was offered 100/. for it." 

 Mr. Cusel is long since rieaH, and what became of his picture I 

 know not. After Mr. Bauer's death, in 1840, these two pictures 

 came into the possession of his friend, Mr. Robert Brown, and 

 I believe are now in the British Museum. 



If you consider what I have now stated worthy of a place 

 in Nature, it is at your service. J. Smith 



Park House, Kew, October 9 



The Portrait of Tycho Brahe 

 In reference to the portrait of Brahe engraved in Nature 

 (vol. XV. p. 406), and to Mr. Dreyer's remarks on it (vol. xv. 

 p. 530), I have the pleasure of sending you the following par- 

 ticulars. In the first place I have permission from Herr Friis, 

 of Copenhagen, ihe learned editor of TkhoitU Bmhei el ad eum 

 doctorum vtrorum Episiohv. Havnicn, 1S76, &c., to publish an 

 important letter from himself : — 



Copenhagen, June 9, 1877 



Dear Sir, — I have seen in Nature (vol. xv. p. 405) an 

 article on Tycho Brahe, with a portrait of him after a painting 

 in your possession. On that account I take the liberty of 

 addressing myself to you. 



In a book printed in Copenhagen in the year 1668 is men- 

 tioned a portrait of Tycho Brahe which once belonged to King 

 Frederick III., and which, no doubt, has had an emblematic 

 figure and inscription similar to that of the portrait you own. The 

 title of this book is " Inscriptiones Haffnienses latinae, danicae 

 et germanics una cum inscripiionibus Am.igriensibus, Urani- 

 burgicis et Stelljeburgicis, &c., edi curivit Petrus Johannis 

 Resenius," and in that you read at page 335 the following : — 



"Sub pyramide tegumento quodam cooperta ad effigiem 

 ejus quEe in Augusiissimi Regis Dinia; Friderici III. Bibliotheca 

 hodie reservatur depicta haec legitur inscriptio : — 



Stans tegor in solido ventus fremat ignis et unda 



Vandesbechi 



an. mdxcvii quo post divtinum in patria e.\ilium demum 



pristin.e lieertati restitutus fui 



Tycho Brake, Or. 



On leaving Denmark T. Brahe rent his portrait to his fiiend, 

 the learned Holger Ro»enkrantz. This has, I suppose, been 

 one resembling the one you now possess, even if it should not be 

 just the same. Compare T. Brahe, "Astronomic instauratse 

 mechanica." Wandesburgi, 159S, fol4. 



The German letters on the order M. H. Z. G. A. indicate 

 Frederick the Second's motto : My hope (is) in God alone (Maine 

 Hoffnung zu Gctt alleio), which is often seen in buildings, &c., 

 from his time. 



If you will be kind enough to send me a photograph of the 

 before-mentioned portrait, I should feel very grateful to you, 

 as I have made the biography of T. Brahe my special study, and 

 just recently began to publish his correspondence with his learned 

 contemporaries. 



Hoping that you will not deny me this favour, I am, dear sir, 

 Yours obediently, 



F. R. Friis 



Cortadelers Gide, 7, Copenhagen 



I have referred to an exquisite copy of the Inscriptiones 

 Hafinienses, from the library of Colbert, belonging to Chetham's 

 Library, in this city, and on the same page referred to by Herr 

 Fiiis I find a poem by Oliger Rosenkrantz addressed to T. Brahe, 

 and prefixed to the Mechanica, of which the last two lines are 

 very interesting, as alluding, in ray opinion, to the emblem on 

 my portrait. They are : — 



" Pectora quam Divi dispensant tramite justo, 

 Stansq. vado /hicius, imbres etjlainitiii teinnt.'* 

 I wish to add a few remarks, and before I proceed farther I 

 would observe that in your engraving the dress o( Brahe is not 

 given correctly, not from any fault ol yours or of your engraver, 

 but because the detailed drawings sent in answer to a request 

 from him to me for details did not reach him until the plate was 

 too far advanced. I have had the picture re-photographed, the 

 photograph worked upon from the picture in a strong light, and a 

 satisfactory result will be published in the Memoirs of the Literary 

 and Philosophical Society of Manchester, and also, I believe, in 

 Herr Friis's very interesting and important work, two fasciculi of 

 which he has kindly sent me. 



