412 



THE BEITISH ASSOCIATION FOE THE ADVANCEMENT OF SCIENCE. 



[1855. 



Tvards filled with calcareous spar, and often presenting a beautiful ap- 

 pearance ivben examined ivith the microscope, on account of their 

 number and regularity, and showing faults of 1-lOOth of an inch, or 

 much less. These are totally distinct from slaty cleavage, -which can 

 be studied to great advantage in such limestoues as have that struc- 

 ture. The author has proposed a theory to account for this, and has 

 shown, that the rocks that possess it have been so much compressed, 

 as shown by a great variety of facts, that the positions of their ultimate 

 particles would be changed in such a manner as give rise to precisely 

 such structure as that which produces cleavage. That this would be 

 a necessary result may be proved both by calculation and experiment. 

 In the case of limestones, it is impossible to suppose that any other 

 than a mechanical cause can have developed the structure seen with the 

 microscope, because the particles whose position has been changed are 

 fragments of organic bodies, and not crystals. Besides this change of 

 position, in many cases minute organic fragments, whose original form 

 and structure are well known, are greatly compressed in the plane of 

 cleavage, as shown by the change in their form and stiucture; and 

 even crystals of dolomite are broken up, elongated, and their crystal- 

 line cleavage planes bent, thus showing that the rock was in a consoli- 

 dated condition when the change of dimensions occurred, but that the 

 pressure was so intense, and acted so gradually, that the whole mass 

 of rock gave way like iron malleable substances, by the movement of 

 the particles one over another. 



On Aurora Borealis. — By Admiral Sir John Ross. — The communi- 

 cation I had the honor of making to the British Association at Belfast, 

 on the interesting subject of the Aurora Borealis, being verbal, and 

 therefore not entitled to a notice in the Association's valuable trans- 

 actions of that period ; but having subsequently repeated the experi- 

 ments I then verbally mentioned, I can now confidently lay the account 

 of them before the public, trusting that, when taken into consideration, 

 they will be found corroborative of the theory which I published in the 

 year 1819, and which led to a controversy that shall be hereafter men- 

 tioned. It having occurred to me that if my theory was true, namely, 

 " That the phenomena of the aurora borealis were occasioned by action 

 of the sun, when below the pole, on the surrounding masses of colored 

 ice, by its rays being reflected from the points of incidence to clouds 

 above the pole which were before invisible," the phenomena might be 

 artificially produced ; to accomplish this I placed a powerful lamp, to 

 represent the sun, having a lens, at the focal distance of which I placed 

 a rectified terrestrial globe, on which bruised glass of the various col- 

 ours we had seen in Baflfin's Bay was placed, to rejiresent the coloured 

 Icebergs we had seen in that locality, while the space between Green- 

 land and Spitzbergen was left blank, to represent the sun. To repre- 

 sent the clouds above the pole which were to receive the refracted rays, 

 I applied a hot iron to a sponge, and, by giving the globe a regular 

 diurnal motion, I produced the phenomena vulgarly called the " Merry 

 Dancers," and every other appearance exactly as seen in the natural 

 sky, while it disappeared as the globe turned, as being the part repre- 

 senting the sea to the points of incidence. In corroboration of my 

 theory, I have to remark that, during my last voyage to the Arctic 

 Begions (1850-51), we never, among the numerous icebergs, saw any 

 that -were coloured, but all were a yellowish white ; and, during the 

 following winter, the aurora was exactly the same colour ; and, when 

 that part of the globe was covered' with bruised glass of that colour, 

 the phenomena produced in my experiment was the same, as was also 

 the Aurora Australis, in the Antarctic regions, where no colom-ed ice- 

 bergs were ever seen. The controversy to which I have alluded, was 

 between the celebrated Professor Schumacher of Altona, who supported 

 my theory, and the no less distinguished M. Arago, who, having op- 

 posed it, sent M. Gimard Martens and another to Hammerfest, on pur- 

 pose to observe the aurora and decide the question. I saw them at 

 Stockholm on their return, when they told me their observations tended 

 to confirm my theory ; but theii' report being unfavorable to the expec- 

 tations of M. Arago, it was never published , neither was the corres- 

 pondence between the two Professors, owing to the lamented death of 

 Professor Schumacher. I regi'et that it is out of my power to exliibit 

 the experiments I have described, owing to the peculiar manner in 

 which the room must be darkened, even if I had the necessary appara- 

 tus with me ; but it is an experiment so simple that it can easily be 

 accomplished by any person interested in the beautiful phenomena of 

 the Aurora Borealis. 



Mr. Robert Macpberson, of Eome, had succeeded in obtaining beautiful 

 photo-lithographs, — specimens of which had been hung up in the 

 Photographic Exhibition in Buchanan-street. The steps of the process 

 are as follows: — 



1. Bitumen is dissolved in sulphuric ether, and the solution having 

 been mixed with a small quantity of some soapy substance, is poured 

 upon a lithographic stone previously placed upon a levelling stand. 

 The ether quickly evaporates and leaves a thin coating of bitumen 

 spread uniformly over the stone. This coating is sensitive to light, a 

 discovery made originally by M. Niepce, of Chalons. 



2. A negative on glass or waxed paper is applied to the sensitive 

 coating of bitumen, and exposed to the full rays of the sun for a 

 period, shorter or longer according to the intensity of the light, and a 

 faint impression on the bitumen is thus obtained. 



3. The stone is now placed in a bath of sulphuric ether, which 

 almost instantaneously dissolves out the bitumen which has not been 

 acted upon by light, leaving a delicate picture on the stone, composed 

 of the bitumen on which the light has acted. 



4. The stone after having been carefully washed, may be at once 

 placed in the hands of the lithographer, who is to treat it with gum 

 and acid, after which proofs may be thrown off by the usual process. 



Professor Eamsay then proceeded to state that the above process, 

 modified, had been employed with success to etch plates of copper or 

 steel : 



1. The metal plate is prepared with a coating of bitumen precisely 

 in the manner described above. 



2. A positive picture on glass or paper is then applied to the bitu- 

 men, and an impression is obtained by exposure to light. 



3. The plate is plunged into a bath of ether, and the bitumen not 

 acted upon by light is dissolved out. A beautiful negative remains 

 on the plate. 



4. The plate is now to be plunged into a galvano-plastic bath and 

 gilded. The gold adheres to the bare metal, but refuses to attach 

 itself to the bitumen. 



5. The bitumen is now to be removed ^entirely by the action of 

 spirits and gentle heat. The lines of the negative picture are now- 

 represented in bare steel or copper, the rest. of the plate being covered 

 with a coating of gold. 



6. Nitric acid is now applied as in the common etching process. 

 The acid attacks the lines of the picture formed by the bare metal, 

 but will not bite the gilded surface. 



Tliornio^eiiic Apparatus* 



Process for obtaining Lithographs hy means of Photography. — Pro- 

 fessor Ramsfr.y, F.Pv.S., of Glasgow, described a process by which 



For some time past there has been a machine at work on the Quai 

 Talony, at Paris, which furnishes a considerable quantity of steam 

 without any other source than that of friction. The machine consists 

 of a cylindrical heater 2 metres long, 50 centimetres in diameter, having 

 throughout its whole length, placed in its centre, a conical tube. The 

 water, which is reduced to vapour, fills the void space between the 

 inner walls of the tube or cylinder and the outer walls of the conical 

 tube. Into the conical tube is passed a cone of wood, covered 

 -throughout with a braid of hemp rolled upon it spirally. The wooden 

 cone is traversed by an iron axis, and fills exactly the interior capacity 

 of the tube, so as to rub constantly against its walls. It is put in 

 motion by a fall of water from the Canal St. Martin, so as to make 

 about 400 revolutions per minate. The heat produced by the friction 

 is sufficient to convert the water contained in the cylinder into steam. 

 A thermometer placed within the boiler indicates, at the end of a cer- 

 tain time, a temperature of 130° C. The boiler is strengthened in the 

 ordinary way, and is fui'nished with safety-vale, stop-cocks, a float, 

 manometer, &c. The vapour reaches a pressure of nearly two and a 

 half atmospheres. A lubricating apparatus constantly conveys to the 

 envelope of the wooden cone the oil required to permit of its surface 

 moving upon that of the interior of the conical tube. This machine 

 holds 400 litres of water. To set it in action requires the power of two 

 horses, it then produces sufficient steam to drive a one-horse engine. 

 The inventors, MM. Beaumont and Major, hope thus to be able to 

 utilise the force of falling water, and convert it into heat. This ma- 

 chine was at work nt the Crystal Palace of Paris. 



