52 



SCIENCE, 



[Vol. VI., No. 128. 



under a slight pressure, and without apparent loss, 

 into the glass gauge V, set, as shown in the figure, in 

 ajar containing pumice-stone saturated with sulphuric 

 acid, to absorb the water-vapor. It is indispensable 

 to work in absolutely dry air; for otherwise the 

 moisture of the air will condense in the form of an 

 icy film on the walls of the gauge, which will become 

 perfectly opaque. 



It is then only necessary to evaporate the ethylene 

 by means of a rapid current of air or of hydrogen 

 cooled in a second worm, placed in the jar of chloride 

 of methyl, S, to cause the oxygen compressed in the 

 glass tube attached to the upper part of the reservoir 

 O to be resolved into a colorless, transparent liquid 

 separated from the gas above it by a perfectly clear 

 meniscus. By working the pump P, the water acts 

 on the mercury in the receiver O, and forces it into 

 the gauge which contains the oxygen. The gas thus 

 compressed liquefies in the branch of the tube in the 

 gauge V. This tube dips into the ethylene at a temper- 

 ature of — 125°. The mass of liquefied oxygen, which 

 is as limpid as ether, is figured in black in the figure 

 in order that it may be visible. By means of a hydro- 

 gen thermometer, I have measured the temperature 

 of the ethylene, which in one of my experiments I 

 found to be — 123°. I am in hope, that, by cooling 

 the current of hydrogen more carefully, the tem- 

 perature may be still further reduced. The copper 

 worms in which the air and ethylene circulate are 

 dipped into the chloride of methyl, which is rapidly 

 evaporated by a current of air previously cooled. In 

 conclusion, by evaporating liquid ethyl by a current 

 of air or hydrogen much reduced in temperature, its 

 temperature may be reduced below the critical point 

 of oxygen, which in this way liquefies in the clearest 

 form. This experiment is so simple and easy to per- 

 form, that it may enter into the regular course in a 

 laboratory. L. Cailletet. • 



THE FORM OF SHIPS.^ 



In the course of his address, the lecturer briefly 

 explained the great development which the science of 

 fluid resistance had undergone of late years, largely 

 owing to the labors of Stokes, Kankine, and others, 

 but more largely still to those admirable investigations 

 which had been carried out, under the patronage of 

 the admiralty, by the late Dr. William Froude, and 

 subsequently by his son, Mr. R. E. Froude. He like- 

 wise explained the very great effect which those 

 investigations had produced in the royal navy, owing 

 to the judicious and prompt adoption of Froude's 

 results by the admiralty constructors. Stress was 

 laid, throughout the lecture, upon the importance of 

 adjusting the form and proportions of ships, not only 

 to the loads which they have to carry, but likewise 

 to the weight of the materials entering into their 

 structure. It was a common error to judge of the 

 merits of steamships by the relations which exist 



1 From a lecture before the Institution of civil engineers by 

 Sir Edward Reed. 



between their displacement, steam-power, and speed, 

 as expressed by formulae of various kinds. Approxi- 

 mations to the theoretical form of least resistance 

 were sought by some naval designers, and all consid- 

 erable departures from that form were regarded as 

 objectionable. The lecturer, on the contrary, pointed 

 out that no such theoretical form was any true or 

 proper guide fo*r a naval designer, since every change 

 in the average weight of the hull necessitated a corre- 

 sponding change in the form and proportions of the 

 ship ; and the great merit of a designer often was, that 

 he adopted forms differing widely from the abstract 

 forms of the schools, and presenting a very inferior 

 appearance when put into what are known as ' con- 

 stants of performance.' This was illustrated by 

 examples derived partly from actual ships, and partly 

 from calculations made for the purpose. Two actual 

 war-ships were compared, one attaining the high 

 figure of 213 marks when examined by the received 

 formulae, and the other gaining but 172 marks ; yet, 

 in the lecturer's view, the latter was far the better 

 ship, because she performed precisely the same ser- 

 vice as the other, being inferior in no respect, and 

 yet had cost less than the other by £114,000, and 

 expended no more steam-power in attaining an equal 

 speed. The lecturer remarked, that he should prob- 

 ably have regarded the abstract 'form of least resist- 

 ance ' with more respect but for the circumstance that 

 the designing of armored vessels, in which he was 

 much engaged, was "a branch of naval construction 

 of much too concrete and ponderous a character to 

 admit of any dalliance with abstract or fancy forms." 

 He went on to express his regret, that owing largely 

 to the restrictions which granite docks imposed upon 

 naval constructors, and to the absence of iron float- 

 ing docks capable of receiving ships of any form, and 

 owing to other causes likewise, the construction of 

 armored ships — by which he meant ships which had 

 a sufiicient volume protected above the water to keep 

 them afloat and upright while the armor remained 

 intact — had been abandoned, and the first place upon 

 the sea had been offered to any nation which had the 

 courage and the will to assume it. In his opinion, 

 this was a purely voluntary abandonment, and was 

 not the result of any scientific or economic necessity. 

 He admitted that great changes in forms and propor- 

 tions were very desirable in our great line of battle- 

 ships : for example, a great increase of breadth was 

 necessary in order to economize the side-armor, and 

 to keep the ram and torpedo at ample distance from 

 the boilers and magazines, which should be protected 

 by an inner citadel, so to speak, well removed from 

 the outer one. But, so far was true science from 

 presenting obstacles to these and other important 

 changes, it actually invited these very changes ; and 

 increase of beam in particular had been shown by 

 Froude to facilitate the attainment of practical invul- 

 nerability combined with very high speed. Size and 

 cost were among the bugbears of our naval adminis- 

 tration : by the true engineer they were always re- 

 garded as secondary to great and noble objects, among 

 which objects he included the naval pre-eminence of 

 England. At any rate, there was no engineering 



