i I Messrs. Ayrton and Perry on the Determination 



the surgeon's knife, or the soldier's bayonet." This is true, 

 provided the knife and the bayonet are handled with skill and 

 for the benefit of mankind. But does not Major Herschel's 

 review, like his present criticism of our paper, instinctively 

 suggest rather the hewing of the professional fighting man 

 than the courage of the skilful surgeon. 



I. To his first objection, that our doctrine regarding labora- 

 torv teaching is " as erroneous as the design is laudable," we 

 would reply that as our paper was read at the Physical Society, 

 of which many of the Members are teachers of physics, and 

 anxious, like ourselves, to ascertain the best mode of carrying 

 on experimental work in a physical laboratory containing 

 many young students, we considered it not inopportune to 

 mention that some years' practice in laboratory teaching had 

 led us to strongly advocate the plan of students assisting in 

 original investigations, and to deprecate their merely repeat- 

 ing well-known lecture-experiments, very commonly the whole 

 laboratory work a student is set to do. Our concluding 

 remarks were not, as Major Herschel seems to think, directed 

 against practice in the use either of Kater's reversible pendu- 

 lum, or, in fact, of any other standard measuring-instrument. 



II. Your correspondent charges us with " neglect of the 

 commonest and most essential principles of exact experimen- 

 tation." Now, as the Editors of the Philosophical Magazine* 

 have allowed this grave charge, one of the gravest that could 

 be brought against scientific men, to be made in the pages of 

 their Journal, it demands careful consideration. To prove his 

 accusation and to show that he is " not making a random 

 charge," Major Herschel quotes a paragraph from our paper 

 in which we explain that the well-known " corrections for in- 

 finitely small arcs and for the air-friction" are negligible in 

 the case of our long pendulum, " on account of the very small 

 angle through which the pendulum usually swung, and. that 

 the decrement of the amplitude of the vibrations was imper- 

 ceptible even after many swings," and in which we further 

 mention that, fearing the possibility of an " error arising from 

 its flexibility and slight elasticity which would not affect a 

 rigid compound pendulum," we endeavoured to calculate the 

 magnitude of the special possible errors for a long wire 

 pendulum. This Major Herschel frankly states perhaps he 



* [I regret much tlie appearance of Mr. Herschel's letter, not so much 

 "because I believe the writer to be, in the main, wrong on the scientific 

 points discussed in it, as because I do not consider its tone and temper 

 suitable for publication in the Philosophical Magazine. I feel confident 

 that my brother Editors agree with me in regretting for the last-men- 

 tioned reason the publication of the Letter, which took place through an 

 oversight in this respect. — W. Thomsox, Ed. Phil. Mag.'] 



