ON THE STUDY OF PHYSICS. 301 



looking-glass, of her own height; it was required to 

 know how much of the glass was really useful to her? 

 We learned with pleasure the economic fact that she 

 might dispense with the lower half and see her whole 

 figure notwithstanding. It was also pleasant to prove 

 by mathematics, and verify by experiment, that the 

 angular velocity of a reflected beam is twice that of 

 the mirror which reflects it. From the hum of a bee 

 we were able to determine the number of times the 

 insect flaps its wings in a second. Following up our 

 researches upon the pendulum, we learned how Colo- 

 nel Sabine had made it the means of determining the 

 figure of the earth; and we were also startled by the 

 inference which the pendulum enabled us to draw, that 

 if the diurnal velocity of the earth were seventeen 

 times its present amount, the centrifugal force at the 

 equator would be precisely equal to the force of gravi- 

 tation, so that an inhabitant of those regions would 

 then have the same tendency to fall upwards as down- 

 wards. All these things were sources of wonder and 

 delight to us: and when we remembered that we were 

 gifted with the powers which had reached such results, 

 and that the same great field was ours to work in, our 

 hopes arose that at some future day we might possibly 

 push the subject a little further, and add our own vic- 

 tories to the conquests already won. 



I ought to apologise to you for dwelling so long 

 upon this subject; but the days spent among these 

 young philosophers made a deep impression on me. I 

 learned among them something of myself and of 

 human nature, and obtained some notion of a teacher's 

 vocation. If there be one profession in England of 

 paramount importance, I believe it to be that of the 

 schoolmaster; and if there be a position where selfish- 

 ness and incompetence do most serious mischief, by 



