!76 



NATURE 



\Atigust 2, 1877 



experiences when propelling the ship under natural conditions, 

 it follows that the same setting of the shutters which suits a 

 given engine when working with its highest speed and power 

 will also approximately suit it when eased down to its lowest. 



It remains to be explained in detail how it is proposed to 

 carry out the operation in dealing with any given ship. 



The ship, before she leaves the dock for the trial of her 

 machinery, will have the instrument mounted as described, in 

 place of her screw. The casing will be provided with proper 

 apertures, capable of being closed at will, to permit the egress of 

 air and the ingress of water as the dock fills. The casing will 

 thus be in a condition to receive the moment of rotation delivered 

 by the screw and communicate it to the recording apparatus. 



The arrangement of the dynamometric apparatus presents no 

 difficulty. In this, the downward pull delivered by the lever 

 operates vertically on the midiile of a flat horizontal steel spring, 

 which is supported at both ends ; and it is proposed so to pro- 

 portion the spring that its maximum deflection shall be about 

 I A inches. Different springs, however, would be required for 

 engines if of widely different power. 



Reference has previously been made to the amount of heat 

 developed by friction in the friction brake, as probably the most 

 formidable of the objections to its employment when the horse- 

 power to be dealt with is as large as that now contemplated. 

 But it must not be supposed that the absorption of the same 

 amount of work in the instrument that has been described will 

 fail to be converted into the same amount of heat here also. 

 The dynamic theory of heat is unquestionable as a theory, 

 and the quantitative relation of work and heat is known with 

 certainty within far narrower limits than deserve even to be 

 mentioned in reference to the present subject. Although, how- 

 ever, the extinction of say 2,000 horse-power will in fact here, as 

 well as in the friction brake, consist in its conversion into so many 

 units of heat, the circumstances of the conversion are entirely 

 different in the two cases, and the difference is such as to 

 obliterate here the inconvenience which was fatally great there. 

 There, the heat was to be dealt with as being constantly deve- 

 loped between surfaces in close contact and inaccessible to water. 

 Here, it will be making its appearance in the body of a mass of 

 water ; and though the rapidity of the development will be so 

 great that the whole contents of the casing would be quickly 

 raised to boiling heat if the heat had no escape, yet, in the first 

 place, there is a cmsiderable refrigerating power always at work, 

 since the whole casing is enveloped in cold water, and, more- 

 ever, there is no difficulty in creating a constant change of water 

 within the casing sufficient to keep down the mean internal tem- 

 perature to any limit which may be thought proper. For 

 instance, when the instrument is dealing with 2,000 horse-power, 

 the temperature would be kept well below the boiling point if in 

 each minute eight cubic feet of cold water be substituted for the 

 same quantity of the hat contents of the casing, nor would the 

 exactness of the dynamometric action be in the smallest degree 

 impaired by the substitution. 



Mr. Froude in his valuable paper, to which we are glad to caU 

 attention, thus summarises briefly the advantage; which would be 

 derived from the system of submitting marine engines to dyna- 

 mometric trial. It is certain that a very large but unmeasured 

 amount of power is wasted, in friction and otherwise, between 

 the cylinders and the propeller ; and that the amount probably 

 differs, both in respect of difference in type of engine and in 

 respect of goodness of construction and workmanship. The 

 chief difficulties which thus arise are as follows :— 



(i) The speed attained by a given ship, driven by a given 

 indicated horse-power, fails to measure discriminatively 

 the merits of the ship. 



(2) No means exist of testint; which type of engine delivers 



the largest proportion of the power which it indicates. 



(3) No test exists by which to measure concisely the specific 



constructional merit of this or that engine, or to deter- 

 mine the relative constructional merit of the engines 

 supplied by different firms. 

 The dynamometric test would remove at once each of these 

 difficulties, by substituting a final and real test for a collateral 

 and to a large extent a delusive one. For to rely exclusively 

 on the test furnished by the indicator is almost equivalent to 

 testing the power of a horse solely by the quantity of food he 

 consumes and digests, or the efficiency of a boiler solely by the 

 quantity of coal per hour it will legitimately consume on its 

 firebars. 



actuating bevel gear 



Table of Reference Letters used in Diagrams and Drawings. 



A. .Screw shaft. 



B. Turbine. 



C. Casing. 



D. Diaptiragms. 



E. Sliding regulating shutters. 



F. Screws for moving E, governed by telescopic 



controlled from ship's deck. 



G. Lever for holding casing. 



H. Links connecting G with dynamometric apparatus. 

 K. Knife-edged gimbal for carrying strain of tl to spruig. 

 L. Framed radius for guiding K and eliminating oblique strains, 

 M. Dynamometer spring. 

 N. Suspension links carrying the ends of M. 

 O. Feeler conveying elastic motion of M. 

 P. Telescopic rod taking rotation of screw shaft by bevel gear : 



nicating it to integrating apparatus. 

 Q. Motion axis of mtegrating apparatus governed by O. 

 R. Automatic integrator. 

 S. Bell crank for magnifying motion of O and conveying it to paper 



cylinder. 

 T. Paper cylinder recording magnified motion of O. 



The graphic integration o{ the record given by T is comparable with the 

 automatic integration given by R. 

 U. Shed covering integrating apparatus. 

 V. Strong balk brackets upholding U. 



THE COMMISSION OF THE FRENCH ACA- 

 DEMY AND THE PASTEUR- BASTI AN 

 EXPERIMENTS 



IN further reply to a communication of mine to the Academy 

 of Sciences of Paris on July 10, 1S76, and as his latest con- 

 tribution to a controversy which grew out of it, M. Pasteur, at 

 the seance of January 29, 1877, threw down a very definite 

 challenge. 



The discussion was raised according to M. Pasteur by my 

 statement, "that a solution of boiled potash caused bacteria to 

 appear in sterile urine at 50° C, after it had been added to the 

 latter in quantity tufficient for exact neutralisation," and he then 

 said : " I defy Dr. Bastian to obtain, in the presence of com- 

 petent judges, the result to which I have referred with sterile 

 urine, on the sole condition that the solution of potash which he 

 employs be pure, i.e., made with pure water and pure potash, 

 both free from organic matter. If Dr. Bastian wishes to use a 

 solution of impure potash I freely authorise him to take any in 

 the English or any other Pharmacopceia, being diluted or con- 

 centrated, on the sole condition that that solution shall be raised 

 beforehand to \10" Jor twenty minutes, or to \yf for five inmiites. 

 This is clear enough, it seems to me, and Dr. Bastian will 

 understand me this time." 



At the seance of February 12 my reply was read. The 

 essential part of it was as follows :—" During the last week I 

 have repeated my experiments several times, and with a degree 

 of precaution going much beyond the severity of the conditions 

 prescribed by M. Pasteur. ... I repeated them at first with 

 liquor potassa: which had been previously raised to 1 10" C. for 

 sixty minutes, and alterwards with liquor potassje which had 

 been raised, in the same manner, to no" C.for twenty hours. 

 The results have been altogether similar to those produced upon 

 sterile urine by liquor potassae which has been raised only to 

 100°, when added m suitable quantity ; that is to say, in twenty- 

 four to forty-eight hours the urine was in full fermentation and 

 swarmed with bacteria." 



After the reading of this reply, M. Pasteur asked the Academy 

 to appoint a Commission to report upon the subject in dispute, 

 and at the next meeting of the Academy (February 19) it was 

 announced that "MM. Dumas, Milne Edwards, Boussingault 

 sont designes pour constituer la Commission qui sera appelee a 

 exprimer une" opinion sur le fait qui est en discussion entre 

 M. le Dr. Bastian et M. Pasteur." 



The following correspondence then ensued : — 



20, Queen Anne Street, iV., February 21, 1S77 

 Dear Sir,— I was pleased to learn, from the Comptes Rendus, 

 yesterday, that the Academy had appomted you together with 

 MM. Milne Edwards and Boussingault to act as a Commission 

 to "express an opinion on the fact" now under discussion 

 between M. Pasteur and myself. 



I can scarcely suppose that the Commission would deem it 

 expedient to express an opinion on this subject without having an 

 opportunity of seeing both M. Pasteur and myself perform our 

 respective experiments. 



I write, therefore, to inform you that if a convenient time can 

 be arranged, I shall be very happy to come to Paris for three days 



