August 26, 1922] 



NA TURE 



277 



Letters to the Editor. 



The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of NATURE. No notice is 

 taken of anonymous communications.] 



The Influence of Science. 



The ingenious letter under the above heading, on 

 page 180 of Nature of August 5, by that industrious 

 astronomer of Stonyhurst College, Father Cortie, 

 S.J., seems to require some brief notice because of 

 the singular character of the statements made in it. 

 We are asked to believe that Copernicus's "helio- 

 centric doctrine was freely taught, even in ecclesi- 

 astical colleges, until Galileo interested himself as a 

 champion of the system " ; in spite of the admission 

 that after this " truculent and hot-headed contro- 

 versialist " had endeavoured to get the Church to 

 realise that the doctrine was not really antagonistic 

 to Scripture when reasonably interpreted, and after 

 the offended Pope had brought the matter before the 

 Holy Office, that authority determined that " the 

 Copernican system was false and absurd philosophic- 

 ally." And we are also asked to believe that the out- 

 come was merely that Galileo had as a penance "to 

 recite certain prayers, and was sent to a beautiful 

 villa at Arcetri " ; the implication being that there 

 was really no punishment, and that there was no call 

 for anxiety or distress on the part of either him or his 

 daughter throughout the proceedings. 



Yet some of us have learnt from extant documents 

 that Galileo was made to recant, to abjure and curse 

 the theory of the earth's motion, and to promise to 

 denounce to the Inquisitor any one suspected of 

 similar heresy. 



Some rather definite pressure must have been 

 brought to bear upon the old man in order to secure 

 this damning retractation — a retractation which the 

 younger and more energetic Bruno a few years 

 previously had contumaciously refused to make. 

 Perhaps, however, it may be contended that in 

 Bruno's case also the Cardinals " proceeded with all 

 the gentleness and moderation which were compatible 

 with judicial forms ! " If so, it is a comfort to us 

 scientific heretics of to-day that judicial forms have 

 by this time lost some of their virulence and the 

 Holy Office some of its power. The flail of orthodoxy 

 is still wielded in high places, by searchers out of 

 scientific heresy ; but the penalties inflicted are no 

 longer ecclesiastical, and — pace Father Cortie — are 

 less severe. 



On second thoughts it occurs to me that the letter 

 may be intended humorously, in preparation for the 

 suggestion that the Church and the Aristotelian 

 professors had some inkling or precognition of the 

 theory of relativity. Father Cortie summarises " the 

 only proofs that were brought forward " for the 

 heliocentric doctrine ; and doubtless the court con- 

 cluded, as modern self-elected authorities do in an 

 analogous case, that " there is no evidence " for any 

 modification of conservative tradition. 



Oliver Lodge. 



Action of Cutting Tools. 



In Nature of July 22, p. 118, there is an interesting 

 description by Prof. E. G. Coker of experiments in 

 which the strains and stresses of a transparent 

 material (celluloid) in the neighbourhood of the edge 



NO. 2756, VOL. I IO] 



of a cutting tool were made apparent by polarised 

 light. 



It ought to be noticed that the word " cutting " 

 as applied to tools used for metal work (and hard sub- 

 stances), though generally in use, is incorrect, the 

 actual action of such tools being to cause shearing. 



Cutting and shearing differ in that in the former the 

 part removed by the tool is merely bent, while in the 

 latter it is at the moment of formation exposed to 



intense local shearing sufficient to cause permanent 

 set or fracture throughout its whole thickness. This 

 is illustrated in Figs. 1 and 2. 



In connexion with this subject I may refer to a 

 paper of my own (Proc. Roy. Soc, 1882), which, so 

 far as I know, is the only place where the distinction 

 has been made. There are very few tools and very 

 few materials which lend themselves to true " cutting " 

 (e.g. thin-bladed tools and soft substances like animal 

 tissues), and in any attempt to " cut " hard materials 

 the tool is soon brought up by the frictional grip of 



— - • — . — 



1. 3. — OA, normal force on face of tool ; BC 

 frictional force on face of too! ; OC. componei 

 of OA tending to make the tool "' dig"; CC 

 component of BO tending to make the tool lift. 



the material on the blade. In tools for hard materials 

 {i.e. shearing tools) the friction of the shearing on 

 the face of the tool is the chief factor in the deter 

 mination of the angle at which the tool-face should 

 be presented to the work. Any angle will cause the 

 requisite shear, but unless the friction on the face 

 balances the inward component of the force due to 

 its slope, the tool will either tend to " dig " or to re- 

 treat from the material being operated on (see Fig. 3). 



Thus for soft copper or aluminium, for example, 

 where the coefficient of friction is large, the angle 

 should be more acute than for brass, where the friction 

 is much smaller. A. aIallock. 



9 Baring Crescent, Exeter. 



