April 2, 1874] 



NATURE 



421 



follow liim in perceiving. It seems to me that in this case "the 

 unknown quantity " is the application of his story. 



I have to add that Prof. Tail's letter gives the erroneous im- 

 pression that I have made a gratuitous assault upon his views. 

 Contrariwise, I have said respecting them no more than is need- 

 ful in self-defence. A critic who thought me greatly in need of 

 instruction respecting the nature of proof and the warrants we 

 have for our ulti.iiate scientific beliefs, quoted, for my benefit, the 

 foregoing passage from Prof. Tait ; and he did this in a manner 

 implying that when he liad told me what Prof. Tait said, there 

 remained for me no alternative but to abandon my position. As 

 I did not coincide in his general estimate of Prof. Tail's dicla, 

 and as this particular question is one of some philosophical inte- 

 rest, I thought it woilh while to justify my own belief, and, in 

 so doing, was obliged to assail that of Prof. Tail. 



In Prof. Tail's desire to avoid controversy I quite sympathise. 

 Though sometimes scarcely avoidable, it entails, as I know too 

 well, a grievous loss of time. P)Ut as Prof. Tait decided not to 

 answer, I think it would have been belter to keep silence abso- 

 lutely, rather than to try and dispose of the mailer by tearing a 

 sentence from its context, and telling, a propos cf it, a story not 

 to the point. 



Alhena-um Club, March 30 IIerisert .Spenxer 



Herbert Spencer versus Sir I. Newton 



Prof. Tait is not tlie only one who has to complain of hard 

 treatment in the pamphlet by Mr. Herbert .Spencer, referred to 

 in the Professor's letter of last week. As the unlucky author of 

 the obnoxious criticism that gave rise to the pamphlet in question, 

 I of course come in for a lion's share of the abuse ; but neither 

 Prof. Tait nor myself are, after all, treated so cruelly as is New- 

 ton, who, though his life v.'as spent in maintaining the experi- 

 mental character of all physical science, is cited as an authority 

 for the a priori character of the most important of all physical 

 truths — the well-known Three Laws of Motion. 



Mr. .Spencer had asserted that these Laws of Motion are 

 a priori truths, and had supported this s'.atement by alleging 

 that Newton gave no proot of them, and therefore intended 

 them to be so regarded. After sheltering myself under ihe au- 

 thority of Professors Tait and Thomson, I answered that " the 

 whole of the Fiincipia was the proof," whereon Mr. Spencer 

 replies as follows : — 



"I have first to point out that here, as before, the reviewer 

 escapes by raising a new issue. I did not aik what he thinks 

 about the Principin and the proof of the laws of motion by it ; 

 nor did I ask whether others, at this day, hold the assertion of 

 these laws 10 I e justified mainly bv the evidence the sobr 

 system affords. I asked what Newton thought. The reviewer 

 had represented the belief that the second law of motion is know- 

 able li/r/c';/ as too absurd even for me openly to enunciate. I 

 pointed out that since Newton enuncia'es it openly under the 

 title of an axiom, and oflCers no proof whatever of it, he did ex- 

 plicitly what I am blamed for donig implicitly. And thereupon 

 I invited the reviewer to siy what he thought of Newton. In- 

 stead of answering, he gives me his opinion to the effect that the 

 laws of motion are proved tme by the truth of the Priiicipia de- 

 duced from them. Of this hereafter. My present purpose is to 

 show that Newion did not siy this, and gave every indication of 

 thinking the contrary. He does not call the laws of motion 

 'hypotheses ;' he cdls them 'axioms.' He does not say that he 

 assumes them to be true proz'isioually^ and that the warrant for 

 accepting them as actually true will be tound in the astronomi- 

 cally-proved truth of the deductions. He lays them down just 

 as mathematical axirms are laid down — posits them as truths to 

 be accepted a priori, from wliich follow consequences which 

 must therefore be accepted. And though the reviewer thinks 

 this an untenable posit on, I am tjuite content to range myself 

 with Newton in thinking it a tenable one — if, indeed, 1 may say 

 so witho it undervaluing the reviewer's judgment." 



To the sneer in the last sentence, and the remark that follows 

 to the effect that the reviewer had evaded an issue " which it was 

 inconvenient for him to meet," I shall reply by recommending Mr. 

 Spencer to dogmatise either less elaborately or less rashly about 

 the views of a philosopher like Sir I. Newton, whose works are 

 so accessilile and wht se style is so clear, and at once pass on 

 to call his attention to two passages in Newton's letters to Roger 

 Cotes, who was at the time superintending the printing of the 

 Friticipia. 



In speaking of the special sense in which he used the word 



"hypothesis" — a sense which quite justified him in saying of 

 himself " hypotheses non fingo" — Newton says : — • 



" In experimental philosophy it is not to be taken in so large 

 a sense as to include the first Principles or Axiomes which 1 call 

 the liuus of Motion. These Principles are deduced from pheno- 

 mena and made general l>v Induction, which is the highest evidence 

 that a Proposition can have m this Philosophy." (Letter Ixxxi., 

 edited by Edleston.) 



And in the next letter he says : — 



"On Saturday last I wrote to you representing that Experi- 

 mental philosophy proceeds only upon Phenomena and deduces 

 general Propositions from them only by Induction. And such 

 is the proof of mutual attraction. And the arguments for y^ 

 impenetrability, mobility, and force of all bodies, and /or the 

 laws of motion are no belter." 



I must confess to feeling a difficulty in reconciling the above 

 extracts with the view that Newton posits the laws of motion 

 "as truths to be accepted d priori." 



The Author of the Article in the 



British Quarterly Review. 



An Experiment on the Destructive Effect of Heat upon 

 the Life of Bacteria and their Germs 



I recently carried out an experiment which I shall not soon 

 have the opportunity of repeating, and which I am consequently 

 anxious to put on record. It is probably now familiar to those 

 interested in the matter, that the experiments of Dr. Sanderson 

 have established the fact that in an infusion of turnips and cheese 

 prepared as directed by Dr. Bastian, heating to a temperature 

 of 102 C. is sufficient to prevent the subsequent development of 

 life (Bacteria) in the infusion even when the exposure to that 

 temperature is only maintained for a few minutes. Boiling for 

 five or ten minutes, according to Dr. Sanderson, is not sufticient 

 to prevent the subsequent development of Bacteria, but .accord- 

 ing to the experiments of Dr. Pode and myself, boiling for ten 

 minutes or a quarter of an hour ;j sufficient, provided that care 

 has been taken to exclude visible lumps of cheese, and when the 

 infusion is enclosed in a tube which tube is submerged in boiling 

 water. Further, Dr. Sanderson has stated the following most 

 important result, namely, that exposure to the boiling tempe- 

 rature (100° C.) was in all cases sufficient to prevent the subse- 

 quent development of Bacteria if it was carried on for so long as 

 one hour. 



This being the case, it occurred to me that since in all pro- 

 babihty Bacteria and their germs, or spores, are killed by 

 through- heatiiiff to a temperaiure a little below 70° C. (as 

 estabhshed by various experiments in regard to Bacteria, 

 but not in regard to possible germs, and admitted by both 

 sides in the controversy as to iheir biogenetic or abiogenetic 

 origin), it is desirable to recognise in our experiments the 

 two distinct factors of this through-heating to any given tem- 

 perature — namely, (l) the temperature to which the infusion 

 to be healed is to be exposed ; and (2) the length of lime during 

 which it is exposed to that temperature. If one of these vari- 

 ables — the time — be taken as a horizontal, and this hne be 

 divided into equal spaces represen'ing periods of five minutes — 

 whilst the perpendicular represents the range of temperature 

 divided into degrees from 65° C. to 120° C — and if the results 

 of observations with a given infusion indicating the time of 

 exposure to a particular degree of temperature requiied in order 

 to prevent the subsequent development of Bacteria be marked 

 off on such a scheme, we should expect to obtain a series of 

 points defining an asymptotic curve, the lime required at the 

 highest temperature being infinitely small, and at the lowest 

 temperaiure infinitely gre.it. This curve would vary in its 

 character according to the propeities of the infusion made use of. 

 It was my intention to determine the principal points in this 

 curve for Dr. Bastian's turnip and cheese infusion, but at pre- 

 sent I have only made a tentative experiment at a low tempe- 

 rature. Using tubes of quarter-inch bore and three inches in 

 length half filled with Dr. Bastian's infusion, and then submerged 

 in water maintained at the desired temperaiure, I found that 

 exposure for six hours to a temperature of 75° C. was sufficient 

 to prevent the subsequent development of Bacteria. The same 

 infusion enclosed in a similar tube and not heated at all, teemed 

 with living Bacteria after four days ; the same infusion boiled for 

 ten minutes in an open lube remained barren. I submit this 

 plan for a series of experiments to the readers of Nature, 

 without attaching mnch importance to the single but definite 

 result which is above recorded. 



