372 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[November, 



ture; a condition which justly and generally considered the reverse is 

 of what it should be. 



But by far the most important and injurious are the effects which 

 heat produces on the air with respect to the quantity of aqueous 

 vapour which it contains, for on this depends its power to absorb more, 

 or to precipitate that which it holds. According to Dr. Dalton, the 

 amount of aqueous vapour which the atmosphere can contain at any 

 given temperature in a state of invisible steam or vapour, is a fixed 

 and definite quantity for that particular temperature. If that tempe- 

 rature be lowered, the point of saturation is also reduced, and the 

 particles of vapour losing a portion of their repulsive power, coalesce 

 and form sensible humidity or dew. If, on the contrary, the tempe- 

 rature of air be raised above any given point of saturation, the con- 

 stituted tendency of water to become vapour is permitted to take 

 effect, with an energy proportional to thp increase of heat; hence the 

 dessication of all surfaces exposed to its influence proceeds at a rapid 

 rate, when they are immersed in air raised much above the tempera- 

 ture of the atmosphere. At all times and places the atmosphere is 

 generally at or near the point of saturation with aqueous vapour. 

 Taking two rather extreme cases, Glasgow in Scotland with a humid 

 state of air, and Funchal in the island of Madeira, the mean tempe- 

 rature of which are 47° 75' and 66° 3', the mean dew points are 45° 

 and 61°, indicating forces of elastic vapour of 0*3 and 0*538 inches of 

 mercury, all respectively. We thus see in a moist and also in a dry 

 climate of great salubrity the near approach of the air to saturation 

 with aqueous vapour, so that its general tendency to absorb water is 

 not great. 



It will probably be thought by some, that the general state of the 

 atmosphere in the consideration of this subject, is inapplicable; but 

 it should be recollected that the same wisdom which contrived the 

 organization of all living beings made also a state of atmosphere 

 adapted to that organization. 



Now, suppose air in the cold of winter at a temperature of 20' 

 raised to that of 70°, by passing over coils of heated iron, or in any 

 other way, it mnst absorb with avidity, everv particle of moisture 

 thinly spread over large surfaces. Having just been transferred from 

 an atmosphere of 20°, it could not be much more than saturated for 

 that temperature; and consequently the heat has produced a condi- 

 tion of air which is nowhere to be found in nature, unless, indeed, we 

 except the sirocco of the arid sands in Western Africa. 



Persons who pass large portions of their time in apartments heated 

 and ventilated in this way, feel extreme dryness of the skin, fulness 

 and throbbing about the head, soreness of the eyes, a dry and kind of 

 asthmatic condition of the mucous surfaces, general excitement, and 

 in some degree prostration of strength. 



Medical men have frequently employed hot air baths for their sti- 

 mulating effects; but that which generally exercises a beneficial power 

 in extraordinary states, as in disease, must surely have a deleterious in- 

 fluence when permanently in operation, even in a less degree than that 

 commonly employed for medical purposes, and especially in states of 

 bad health of an opposite character to those for which it is employed 

 as a remedial agent, as for instance, when any tendency to apoplexy 

 exists. 



It has been proposed to remedy the dry state of hot air, by evapo- 

 rating water, conveying steam with the heated air, &c. ; but all such 

 means are too complicated for the intended purpose, and incapable of 

 adaptation to the circumstances of the case. For during the time 

 when the apparatus is not in use, if the air had been near a state of 

 saturation with aqueous vapour during the day, a large precipitation 

 of dew would take place on cooling, and also during the day, owing 

 to considerable changes of temperature. From these facts and cir- 

 cumstances it is evident that an ordinary fire fulfils all the principal 

 objects of warming and ventilation, better than any of the unnatural 

 modes which science, ingenuity, necessity, or desire for novelty has 

 yet given birth to. 



W. G. 



THE FORMS OF SHIPS. 



The great importance of naval architecture induces us to return to 

 the report of experiments conducted by a committee of the British 

 Association for the Advancement of Science, which was read at their 

 last meeting at Cork. The account copied into the last number of our 

 Journal, from the Athtnceum, was chiefly limited to the notice of the 

 experiments themselves, and merely adverted casually to the deduc- 

 tions founded upon them, without describing the form of least resist- 

 ance which the committee recommend as the result of their five years' 

 labours. We have since been supplied with a further account of Mr. 



Scott Russell's exposition, and as the experiments have been more 

 numerous, and have been conducted on a larger scale than any pre- 

 viously made on the subject, we think it desirable, in the absence of 

 the voluminous report of the committee and drawings, which may not 

 be published for years, to state at least some of the results of these 

 long-continued and costly experiments. 



In Mr. Scott Russell's exposition of the labours of himself and Pro- 

 fessor Robison, after mentioning minutely the mode in which they had 

 conducted their experiments, and their results, he proceeded to de- 

 scribe the form of construction which they had determined to be the 

 best, not only as offering the least resistance to motion through smooth 

 water, but also as best adapted for rough seas. It is to be regretted, 

 however, that in this, the most important part of his exposition, Mr. 

 Russell was less explicit and not so minute as in describing the pre- 

 liminary experiments. He stated facts, but did not explain the prin- 

 ciples by which they were regulated, therefore it is difficult from one 

 isolated form of construction, which was all he exhibited, to determine 

 how far it is adapted to vessels of other sizes. He observed, that the 

 great point which, in the first instance, was endeavoured to be gained 

 was to get rid of the wave at the bow, which has the same effect in 

 retarding a vessel as if it were immersed so much deeper in water. 

 It was found that this object might be attained by lengthening the 

 ship, and that whenever speed was required, there must be an absolute 

 length without regard to breadth. 



Mr. Russell having stated that each velocity has a corresponding 

 form and dimension peculiar to that velocity, he exhibited the form of 

 the light-water line of a steam-vessel intended to be propelled with a 

 velocity of 17 miles an hour, and explained the mode of constructing 

 it. Suppose the breadth, C D, of the vessel to 

 be 25 feet, there must be set off forward from 

 the greatest midship-section 120 feet, and for 

 the after-part, S5 feet. To make room for the ' 

 engines, there is no objection to putting in a 

 piece in the middle of the vessel, called the 

 middle-body, of equal width to the greatest 

 midship section. On half the breadth of the 

 vessel, fore and aft, describe the semicircles C,D, 

 E, G. Divide the fore part, o A, into a given 

 number of equal parts, and divide the semicir- 

 cles also into the same number of parts; in the 

 accompanying diagram, we have divided them 

 into not more than four, for greater distinctness. 

 Then draw lines parallel to the keel, A B, 

 from the divisions o, v, o, of the semicircles to 

 the corresponding divisions p, p, p, and r, r, r, 

 of the keel, and the points where the lines 

 intersect show the form of water-line required. 

 The form thus attained, it will be observed, 

 is very sharp both fore and aft, though the 

 after part, or run, being shorter, is necessarily 

 more full than the entrance of the vessel. 

 This form is much opposed to the ordinary 

 practice inasmuch as the line is hollowed 

 out or partly concave, instead of being of the 

 convex form, or full bow, which old ship- 

 builders so much admire. 



Having thus described the form of the light- 

 water line, Mr. Russell promised to give the 

 view he entertained of the principle on which 

 the superiority of its construction depended; 

 in this particular, however, he failed to make 

 himself very clearly understood. He first 

 alluded to the notions entertained of the man- 

 ner in which the water is displaced by the 

 motion of a vessel. It is commonly supposed, 

 by ship-builders, that the water passes round 

 the vessel ; some imagine that the. fluid is rolled 

 under it; whilst, according to the French phi- 

 losophers, the impact of water obeys the same 

 laws as the impact of solid bodies, and the 

 water is reflected from the bow at an angle equal 

 to the angle of incidence. From the latter as- 

 sumption they deduced that a round full bow is 

 best adapted to meet with least resistance. It 

 had been proved, however, in the course of 

 these experiments, that the particles of water 

 displaced by the bow of a vessel move into new 

 places, that peculiar motions are given to them, 

 and that they never return to their former 

 positions. The motion of displacement, also, 



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