300 



THE CIVIL ENGINEER AND ARCHITECTS JOLRNAL. 



[Septembkb, 



iiios|ihci"e has been thoujrlit to be sufficient in most cases; and the 

 followinf; airan^'iMiiejit of the machinery has been adopted for a 

 one-horse power, wliiih may be expected to furnish a room witli 

 about HI) cubic feet of air per minute, cooled 16° to 20' below tlie 

 atniospliere outside. A double-actin<f air-))unip, 9 inch diameter, 

 and IH incli stroke, niakinj; 60 double strokes ])er minute, with a 

 jacket of cold water round tlie cyliiuler to mitigate the heat of 

 friction, forces the air into the lower end of a coil of copper tube, 

 contained in a tul) of water, 3 feet diameter and 5 feet high, where 

 t)ie coidiiig is effected. At tlie upper end of the tube is a safetv 

 valve, which permits an escape of the confined air, when it 

 exceeds 7 lb. on the square inch, into a larger tube, which at once 

 londucts the now coided air into the desired apartments. Where 

 the work is constant, the piston should have a metallic packing, and 

 the usual contrivance in stills should be adopted for changing the 

 water of the worm tub. 



A, air pump; B, still worm tub; c, inlet air-valve; d, outlet valve for compressed 

 air . €, wurni-lub ; /, chamber for corapresseri and contcd a'r; g, loaded valve to refrulate 

 compr.s^ioii; ft, tube for expitnded air; J. valve to regulate eipunaion ; A', tube for ton- 

 Teyint; tbe expanded air to the room to be cooled. 



The room to be filled with cold air should either bo surrounded 

 by a wall, unbroken by doors and windows, to at least 1 feet in 

 lieiglit; or, which would be the better plan, shiuild be sunk that, 

 or a greater depth, in tlie ground. For the exit of the warm air, the 

 opening of an upper sash of a window will be quite sufficient. 



U'ith regard to the power which is necessary to work the pump, a 

 small steam-engine, though convenient as subserving a residual 

 ilifficulty to be presently mentioned, would perliaps hardly be suit- 

 able but for a very few spots in India. A pair of bullocks would be 

 the power most easily procurable in the greatest number of places, 

 and at a very low rate. The manufacturer here should therefore 

 scml out with the pump a portable "horse-work," i. c. a small mill- 

 work, such as horses or oxen might be applied to, and which by 

 means of wlieels and pinions or bands, should produce the necessary 

 quickness of motion for the cranked axle of the pump. Where 

 water-])0wer is available, it should on no account be neglected; 

 and in the majority of cases it is probable that the wind might be 

 turned to good account. 



So much for the sort of power by means of whicli the cooling 

 a))paratus is to be worked. But this being supposed to answer, a 

 residual difficulty may be expected to arise in many cases — -the 

 cooled air will be found unpleasantly moist. This may be cor- 

 rei-ted liy the natural tendency of air to deposit its moisture on 

 metallic bodies colder than itself; and by making the tube which 

 conveys the cooled air into the room pass through a still c<dder ves- 

 .■^el of water, the moisture will be condensed on the inside surface 

 of the metal, arul may be conducted away by a subsidiary pipe. 

 "\\'liere mechanical power is cheap, this vessel of water may be kept 

 iit llie low temperature by passing through it air which has been 



comjuessed to a still greater degree than that conveyed through the 

 tubes to the rooms; or where fuel is cheap, by the liquefaction of salts. 

 Of this kind, a trreat number of freezing mixtures have lately been 

 produced, and the exact constituents have been kept secret by the 

 manufacturers; but it is probable that no more convenient combi- 

 nation can be employed than salt])etre and sal-ammoniac, both 

 easily procureable in India; and, having the unusual property 

 amongst salts of crystallising separately from the combined solu- 

 tion, they may be used over and over again ad infinitum, employing 

 a fire if natural means are insufficient for evaporating the fluid. 



We thus see that tliere is a natural law which we may avail our- 

 selves of, to cool air to any extent by the employment of mecha- 

 nical power; and simply in compressing air by means of a forcing 

 pump into a closed vessel, which is a good conductor of heat, as a 

 coil of pipe under water; the air will rise in temperature at first 

 to a degree proportioned to the compression, say oO° Fahrenheit 

 above « hatever it was before; so that whether the atnios])here we 

 begin operations in is 70°, or 100% or 120° Fahrenheit in the 

 shade, it matters not to the success of this method. The com- 

 pressed air, which would thus have risen in the intermediate case 

 from 100° to l-0% would by degrees give off that extra heat to the 

 water surrounding the cooler (it is only necessary, it will be ob- 

 served, to have a certain quantity of water of a temperature not 

 above 100°, which in general will not be very difficult to obtain); 

 and if the air then be allowed to escape from the pressure and con- 

 finement into tlie atmosphere, it will fall again 50° below 100°, or 

 be found at 50° Fahrenheit. 



If the air had been allowed to escape immediateli/ after compres- 

 sion, its temperature would not have been altered in the final re- 

 sult, it would have been increased certainly on compression to 150°; 

 but then expanding from there, the cooling effect could only bring 

 it down to 100°. If, however, as described above, we carry off the 

 ejctra 50° liy ronrlndion and riidi<iti(in during the time of the air 

 beiny in thr romjirensed xtnte. then it evidently must issue at the low 

 temperature of 50° Fahrenheit; and if a sufficiently large pump 

 is kept at work, and the cooler of the compressed air be sufficiently 

 extensive, there is evidently no question but that of expense to 

 prevent us from having a constant stream of any amount of air 

 issuing from the other end of the apparatus, and cooled to any 

 extent that may he desiralile. 



This I believe is the first time that this property of air has been 

 put into requisition for any purpose of the sort, but it first 

 occurred to me in South Africa in 184.3. In 1S44 I had a small 

 apparatus made to test this matter experimentally at the Cajje, 

 and a larger one in Edinburgh in 1847; and in this way soon ascer- 

 tained that the quantity of rise in the temperature of air for n 

 small degree of compression was so great (about 30° Fahrenheit 

 for ;j of an atmosphere), that there could be no doubt that when a 

 good arrangement of the machinery had been planned, and «hen 

 it had begun to be manufictured on a large s<'ale, it would lie 

 found to be abundantly witliin the means of most of our country- 

 men in India and in tropical climates. 



Thus I hope that the general problem of cooling the air of 

 rooms in tropical climates, may be considered to have been com- 

 pletely solved, and that by no very e.xpensive means or comjili- 

 cnted apparatus. And should the Society be of the same opinion, 

 anil private gentlemen be disinclined to run the risk of incurring 

 expense for a machine which has never yet been practically tried, 

 then I do hope that some steps may be taken to urge on the 

 honourable East India Company or her Majesty's government, tlie 

 propriety of trying the experiment in some of the large hospitals, 

 where the plan could be so much more efficiently carried out and 

 su])erintendcd than in a private establishment, and where so many 

 of our cinintrymcn may be suffering, and even dying, at this 

 moment sheerly from the effects of too much warmth in the 

 atmosphere. 



ATLANTIC WAVES. 



On Atlantic Waves, their Magnitude, Velocity, and Phenomenon. 

 By Dr. Scorksby. 



DuRi.NG two passages across the Atlantic in 1847-S, I had oppor- 

 tunities for investigating certain elements respecting deep sea 

 waves more favourable than had ever before occurred within my 

 experience in navigation. These observations, it should be noted 

 in the outset, and the results deduced from them, were entirely 

 uninfluenced by, and separate from theory. They form but a con- 

 tribution to this interesting brancli of natural phenomena; but I 

 olier them the more readily from the circumstance of their entire 



