TEACHING PHYSICS. 389 



be without, and no scientific man dare to be without, and to those 

 who have the ability, the opportunity, and the desire, a trust- 

 worthy foundation on which to base their further studies. 



The scheme almost necessarily formed itself into the follow- 

 ing : The student attends a lecture every morning, except Satur- 

 day, at ten o'clock. These lectures, in the present case, are about 

 seventy in number. At eleven o'clock he goes into the laboratory, 

 provided with a few tools ; there he finds the necessary material 

 for making apparatus relating to the lecture. He has also printed 

 instructions directing him how to make and how to use the appa- 

 ratus when made. He finds also working models of such appa- 

 ratus for his guidance. These instructions he carries out under 

 the supervision and advice of a skilled assistant. 



The instruments the student of average skill can and does 

 make under proper instruction with these means are far more 

 accurate than those he is at all likely to be able to buy. I do not 

 say that his divided circles will be as accurate as those of Trough- 

 ton and Sims, nor will his spectroscope compare with one of Hil- 

 ger's, nor his resistance coils with those of Elliott, nor his ba- 

 rometer with the one at Kew ; but I do say that his barometer is 

 a far more exact instrument than one for which he would have to 

 give several pounds ; that his spectroscope will divide the sodium 

 line ; that his coils are true to the thousandth of their nominal 

 value ; that he can determine the wave-length of light to within 

 YoVo- of the truth, the specific heat of a metal to T fo > and the length 

 of a sound-wave to ^^-g- of the truth. The only bought instrument 

 of precision which the student uses in the elementary course 

 is the balance. He has generally, however, acquired some skill 

 with this, and in the manipulation of glass, in the chemical labo- 

 ratory. 



Starting with a tuning fork which is given to him, and the 

 monochord which he makes, the student is able to verify the in- 

 tervals of the gamut as dependent on length of string. He then 

 examines the effects of variation of diameter, of tension, and of 

 weight of the string. 



Tuning forks are, however, seldom exact. The actual pitch of 

 the fork is found by the method of sinuosities. A smoked glass 

 plate is dropped in front of a style on the fork, and so the fork 

 writes its own number. Hence, by means of the length of the 

 resonant cavity, the velocity of sound in air is obtained with some 

 accuracy, and by the method of longitudinal vibrations the ve- 

 locity in wood, glass, and brass, etc., follows. The rule of the 

 transverse vibrations of rods is examined. The production of 

 harmonics on strings, rods, and in tubes is shown, and a number 

 of experiments follow concerning the velocity of sound in differ- 

 ent gases as determined by dust figures. 



