498 



SGimOK 



[N. S. Vol. V. No. lit. 



the discharge of the condenser is exceed- 

 ingly rapid, it has entirely passed before 

 the commutator segment has left the brush 

 leading to the primary. In other words, 

 the condenser brush leaves its commutator 

 segment when both are at 220 volts, and 

 the coil brush leaves its commutator seg- 

 ment when both are at zero. Hence no 

 sparking need occur on the commutator ex- 

 cept the slight spark of making circuit. 



The great increase in voltage at the termi- 

 nals of the secondary over that given by the 

 same coil when operated in the ordinary 

 manner is probably due to the exceeding 

 rapidity of discharge of the condenser, and 

 hence the rapid change in the number of 

 lines of force enclosed by the secondary. 

 For each discharge of the condenser there 

 must be a rise and fall of the current in the 

 primary of the induction coil; but, since we 

 get a uni- direction discharge at the second- 

 ary, one of these alone, either the rise or 

 fall, must be effective. The reaction of the 

 secondary of the coil tends to increase the 

 rapidity of rise of current in the primary, 

 but tends to retard the fall, moreover, at the 

 instant the condenser is connected to the 

 Qoil we have 220 v., the potential of the 

 condenser, applied to a circuit of exceed- 

 ingly low resistance and very small induc- 

 tion, and from this we must get an ex- 

 tremely rapid rise of current. From these 

 considerations alone it appears probable that 

 the secondary discharge is due to rise rather 

 than to the fall of current in the primary. 



The volume of the discharge is so great 

 that the ends of the secondary bristle with 

 brush discharges, even when the terminals 

 are within sparking distance of one another, 

 and great care must be taken in insulating 

 the primary from the secondary. There 

 seems, moreover, to be a continual brush 

 discharge from turn to turn of the primary, 

 the nature of which we are unable to deter- 

 mine. If the iron wire of the core be put 

 in a glass tube, and the primary be wound 



in a single layer about it, and the whole 

 inclosed in a second larger tube, and the 

 space between the tubes be fiUed with oil, 

 the needed insulation is given. 



Charles L. Noeton, 

 Ralph E. Lawrence. 

 EoGEEs Laboratory op Physics, 

 Massachusetts Institute of Technology, 

 Boston, March 5, 1897. 



NEW YORK STATE SCIENCE TEACHERS' AS- 

 SOCIATION, n. 

 [ Continued from p. 4BS. ] 

 Wednesday evening was devoted to the 

 Earth Sciences. Dr. Frank M. McMurry, 

 of the Buffalo School of Pedagogy, read the 

 following paper, written by Professor Ralph 

 S. Tarr, of Cornell. 



Place of the Earth Sciences in the Secondary 



Schools. 



The question is raised again and again, 

 shall the earth sciences (geology and phys- 

 ical geography with their subdivisions) 

 have a place in the curriculum of the 

 secondary school ? and this has been vari- 

 ously answered. Many schools have prop- 

 erly omitted them from the course, and 

 others are thinking of doing so. I say 

 properly, because, as the subjects have been 

 taught in the majority of cases, it is better 

 to omit than to continue them. 



Then again, when the question is under 

 consideration, which of the natural sciences 

 shall have a place in the schools, we very 

 often find the earth sciences excluded, 

 though this was certainly not the case in 

 the report of the Committee of Ten. The 

 reasons given for the exclusion of these 

 subjects from the proposed curriculum are 

 usually two: first, that they are not dis- 

 ciplinary subjects; and second, that for their 

 proper understanding they need too much 

 knowledge of other sciences. The first 

 grows out of a failure to appreciate that 

 there has been progress in the methods of 

 teaching the earth sciences, a progress 



