506 



SCIENCE. 



[N. S. Vol. U. No. 42. 



of. Investigation of rates and temperature 

 coefficients. 



The Zenith Telescope. Investigation of 

 constants. Determination of latitude. 



The Universal Instrument. Refined de- 

 termination of azimuth. Latitude from 

 altitudes of stars. Time from transits over 

 the vertical circle of Polaris, Doellen's 

 method. 



Transit Instrument in the Prime Vertical. 

 Determination of latitude and declinations 

 of stars. 



The prosecution of such a course of study 

 necessarily implies a considerable addition 

 to the student's theoretical knowledge, and 

 concurrently with his instrumental work he 

 should take up in the standard treatises 

 such subjects as precession, nutation, aber- 

 ration, refraction, the reduction of star 

 places, etc.; but we here approach, if indeed 

 we have not already passed, the bounds 

 which separate engineering study from the 

 domain of the professional astronomer. 



The points at which the writer of this 

 paper seeks to place special stress are that 

 a brief course in spherical and practical 

 astronomj' is properlj^ a part of the profes- 

 sional training of everj^ engineer in whose 

 work surveying is to occupj^ an important 

 place, and that this instruction can be ad- 

 vantageously given with no further instru- 

 mental equipment than that possessed by 

 every good school of engineering. 



George C. Comstock. 



Ukiveesity of Wisconsin. 



HOW FAB SHALL THE PERIODIC LAW BE 

 FOLLOWED IN TEACHING CHEMISTKY? 

 More than a quarter of a century has 

 passed since Mendeleeff announced the 

 Periodic Law. Any one who critically sur- 

 veys this period will be forced to admit 

 that this discovery has been the most fruit- 

 ful of results of any since the Atomic 

 Theory, and I believe we are just beginning 

 to realize the value of this Natural Law 



and to have some idea of the fulness of its 

 true meaning. 



Chemists have shown themselves very 

 conservative in the adoption of such dis- 

 coveries and the ordering of theii' science 

 by means of them, but it seems that in this 

 case they have carried their conservatism 

 too far. And perhaps this conservatism 

 has not always been that which springs 

 from a careful guarding against the possibly 

 false and misleading, but rather from mental 

 inertia and a dislike of giving up the old 

 and learning the new. 



The Natural Law, if ti-ue, introduces 

 some most radical changes into the science. 

 It is in a measure subversive of the old. 

 It is impossible to cling to the old system 

 while ascribing high praise to the Periodic 

 Law, as is done in so many of our text- 

 books. 



If this law is true it must dominate all 

 of chemistry. Its statements are funda- 

 mental and all-embracing. It cannot con- 

 sent to share its authority with the old sys- 

 tem. There can be no half-way measures. 

 Just in so far as it is accepted as proved it 

 must be incoi-porated into the science. The 

 custom has been to teach chemistrj^ to be- 

 ginners very much in the old stj'le, and 

 then to give a short time to explaining the 

 Periodic Law, instead of teaching the 

 science with this as the verj^ foundation. 



It is manifestly the duty of a conscien- 

 tious teacher to satisfy himself as to how 

 far this law is true, and then to make all 

 possible use of it in his teaching, as he does 

 of the Atomic Theory itself. If it is false 

 reject it, if true let it be the foundation of 

 your system of instruction. 



Now let me say, at the beginning, that 

 for myself, I regard this law as incomplete 

 in several of its details. But some points 

 of prime importance may be regarded as 

 settled. 



1. That the elements are not distinct and 

 separate individuals, but are more or less 



