IOO 



SCIENTIFIC NEWS. 



[Aug. 3, 1888. 



light is forbidden by law in some countries. Indeed, 

 whatever shines attracts the inmates of the waters; a 

 fragment of a broken plate is a good bait for lobster pots. 



The notion of lighting up the sea for fishing has pre- 

 sented itself to many minds. Three years ago the 

 Talisman drew behind her a lamp immersed some 

 metres in the sea. A short time ago an English scien- 

 tific society set out from Liverpool on board the Hyaena, 

 and tried illuminating the sea to the depth of some 

 fathoms. 



But to convey the electric light to depths exceeding 

 1,000 yards is a much more difficult problem. The first 

 suggestion was to let down an apparatus communicating 

 by a cable with the ship in which the electric current 

 was generated. This proved absolutely impracticable. 

 The sole expedient is a battery let down to the bottom 

 and left in the trap. But then there appeared a new 

 difficulty. The apparatus will have to support a pres- 

 sure of as many atmospheres as there are above it 

 multiples of 32 feet of water. At 4,000 yards it would 

 have to bear, approximately speaking, 400 atmospheres, 

 a pressure which few materials and few connections can 

 support. Dr. Regnard's invention consists in doing 

 away with the pressure at whatever depth, or, at least 

 equalising the inside and the outside pressure. This he 

 effects as follows : — ■ 



The trap which he uses is cylindrical, with three 

 apertures and a door. On the bottom rests a " Cardan " 

 suspension containing a sort of iron pot closed with a 

 lid. This lid closes with iron pins, which press upon a 

 ring of caoutchouc. Into this recipient are put seven 

 Bunsen elements, in which chromic acid is substituted 

 for nitric acid. Each of the cells of these Bunsens is 

 closed with a plate of caoutchouc to prevent the liquids 

 from getting mixed by any sudden movement. All these 

 elements, combined in tension, feed an Edison lamp of 

 12 volts enclosed in solid glass. The inside and outside 

 pressure are equalised by the following arrangement. 

 Above the trap is a balloon of caoutchouc enclosed in a 

 net which supports it during the immersion. A tube 

 leads from this balloon into the interior of the pot con- 

 taining the battery. 



On lowering the apparatus into the sea the balloon is 

 compressed, and it injects into the iron pot so much air 

 that the inside pressure is just equal to the outside 

 pressure. All that is required is to calculate the capacity 

 of the pot so that it may be proportionate to the 

 capacity of the balloon and the depth to be reached. 

 The same principle is applicable to all kinds of apparatus. 



MECHANICAL REFRIGERATION. 



/CONSISTENT with many other theories, and in ac- 

 cordance with the old methods of scientific thought, 

 the idea of " an imponderable fluid " called caloric was 

 used until the end of the last century to explain the 

 phenomena of heat. Lord Bacon, as he is generally 

 called — though his name was either Francis Bacon, or 

 Lord Verulam, for we do not speak of Lord Disraeli — 

 had long before expressed his opinion that heat consists 

 of a " kind of motion or brisk agitation of the particles of 

 matter." In that remarkable work, the Novum Organum, 

 which the classical scholar generally thinks is a dry list 

 of scientific facts, but which is full of quaint ideas and 

 amusing theories, after recounting a number of sources 

 of heat, among which he alludes to the friction of trees 

 rubbing against one another in a high wind, he says : 



" From these examples, taken collectively as well as ( 

 singly, the nature whose limit is heat appears to be 

 motion ; " " the very essence of heat, or the substantial self 

 of heat, is motion and nothing else." Unfortunately 

 there was but little method in the scientific thought of 

 these days, the theory-making was little else than guess- 

 work. Neither enough evidence was collected, nor was 

 sufficient care given, first to sift it, and then to reason . 

 upon it in a really scientific manner. 



Count Rumford and Davy completely disproved the 

 material or caloric theory of heat, and showed by experi- 

 ment that an unlimited amount of heat could be obtained 

 by purely mechanical means. 



According to the old theory, the caloric fluid permeated 

 the substance of bodies, and could be squeezed out, like 

 water from a sponge. The heating of a piece of iron by 

 the blows of a hammer was thus explained. The idea 

 of the presence of caloric in a body was sometimes mixed 

 up with the notion of " latent heat," and some persons 

 have been led to think that because the caloric theory 

 has been completely exploded, that the theory of latent 

 heat is also unorthodox. 



" Science is measurement," and before proceeding to 

 discuss the subject of heat, it is necessary to have some 

 definite ideas about its measurement, and the units by 

 which it is measured. The English unit of heat is that 

 which will raise one pound of water one degree Fahren- 

 heit; strictly speaking, from freezing point to one degree 

 above, for at high temperatures a little more heat is re- 

 quired. If we take a lump of ice weighing one pound, 

 and apply sufficient heat to raise one pound of water one 

 degree, the temperature of the ice will not alter, but • 

 some of it will become melted. On applying another 

 unit of heat, a little more will melt. We should have to 

 supply as much heat as would raise 142 lbs. of water one 

 degree Fahrenheit, or one pound of water about 142 de- 

 grees, before all the ice was melted ; and, until all the 

 ice had disappeared, the temperature of the mixture 

 would remain unaltered. Where has all the heat gone? 

 It has become latent in altering the water from the solid 

 to the liquid state. It exists no longer as heat, but as the 

 energy of motion of the molecules of the water. To 

 freeze the water again, 142 units of heat must be ab- 

 stracted. 



It is easy enough to produce heat by mechanical 

 means, in fact it is impossible to avoid doing so to some 

 extent whenever work is done, for in every machine 

 there is some friction, and where there is friction there is 

 heat. To produce Cold is not so simple. 



Most substances expand when they are heated, and 

 contract when they are cooled. And conversely, when 

 they are compressed their temperature rises, and it falls 

 when they are allowed to expand.* If a piston carrying a 

 bit of tinder be suddenly thrust down a well fitting brass 

 tube, closed at the bottom, the air will be heated enough 

 to set fire to the tinder; such an appliance was once 

 common in Germany. 



If the piston be allowed to spring back at once, the 

 heat which was generated by the compression is absorbed 

 by the air, as it returns to its original bulk. But if, while 

 compressed, it be cooled by a spray of cold water ; when 

 it expands it will be reduced in temperature. On this 

 principle most of the refrigerating machinery on board 

 the ships which carry frozen meat is constructed. The 



* Indiarubber is an exception. If an elastic band be suddenly 

 extended while it is touching the lips it will feel warm, and when it 

 is relaxed it will feel colder. 



