June i, 1915] 



SCIENCE 



825 



larger land mammals of the world, and the 

 peculiar and interesting indigenous faunas of 

 many small islands may still be permanently 

 preserved by prompt protective measures, and 

 not merely state and national action, but as 

 soon as the vs^ar is over, international agree- 

 ments to bring about cooperation for these 

 ends are urgently needed. Future generations 

 Vfill look back on the present time as an age 

 of shameful vandalism as far as nature is con- 

 cerned. Our present imperfect and feebly 

 carried out efforts for the preservation of the 

 most interesting and wonderful of the birds 

 and mammals that still survive are insufficient. 

 They must be on a larger scale and more effec- 

 tively and intelligently conducted tlian at 

 present. It should be the effort of every scien- 

 tific man, and especially of the larger and more 

 influential scientific associations, to bring the 

 seriousness of the situation to public notice 

 and to insist on prompt action. This is vastly 

 more important for zoology to-day than the 

 naming of new subspecies or than disputes over 

 the validity of scientific names, and should put 

 an end to complaints over small personal 

 and temporary inconveniences which regula- 

 tions of the greatest importance may inciden- 

 tally occasion. Willard G. Van Name 

 New Yobk State Museum 



fundamental equations of mechanics 

 To THE Editor of Science: We are greatly 

 interested in the contribution to the teaching 

 of elementary dsmamics made by Professor 

 Kent in his letter to Science appearing in 

 the issue of March 19, in which he presents 

 as the fundamental equation of mechanics 

 V = FTg/W, where F, T and W are, respect- 

 ively, force in pounds, time in seconds and 

 quantity of matter in pounds, g a numerical 

 factor of proportionality and V velocity in 

 feet per second. This equation has the great 

 advantage of avoiding the extremely awkward 

 necessity involved in apparently simpler for- 

 mulations of the experimental laws under con- 

 sideration, of defining force in terms of mass, 

 as so many of the more conservative physicists 

 insist on doing, or of defining mass in terms of 

 force, a thing which many of these conservative 

 physicists seem to consider as the only alter- 



native and which all engineering writers ap- 

 pear to disclaim with equal vehemence. 



There can be no doubt of the difficulty of 

 measuring quantity of matter, that is com- 

 paring the quantities of matter in two bodies, 

 one of which is taken to be a standard, except 

 by resorting to forces acting upon them. On 

 the other hand, there can be no doubt of the 

 inadvisability of attempting to preserve an 

 international prototype force instead of a pro- 

 totjrpe quantity of matter, owing to the proba- 

 bility that secular changes in the elastic prop- 

 erties of material bodies would be vastly greater 

 than changes in their quantity of matter. To 

 be sure it would be possible to define the inter- 

 national prototype force in terms of the gravi- 

 tational relation of a given body to the earth, 

 but this would be open to the same objection 

 as the one that was raised in regard to meas- 

 uring the quantity of matter in a body by 

 resorting to forces. We therefore think that 

 Professor Kent has done well to retain force 

 and quantity of matter as equally fundamental. 



What seems to us as unfortunate is the neces- 

 sity of defining velocity in terms of distance 

 and time. Why not regard all dynamical 

 quantities that are sufficiently distinct to be 

 given different names as equally fundamental ? 

 Why stop with distance, time, quantity o£ 

 matter and force? We see no reason for im- 

 posing on ourselves such a limitation. 



On this principle the equation F = ma, to 

 which Professor Kent objects because it is not 

 true unless we make m an arbitrary symbol 

 for W/g, is open also to our objection that a 

 has been defined in terms of other magnitudes, 

 whereas nature has furnished us with a defi- 

 nite acceleration, that of a body under the in- 

 fluence only of its gravitational relation to the 

 earth at sea-level and latitude 45° as modifled 

 by its tendency to rise due to the rotational 

 motion, which may well be taken as unit accel- 

 eration. 



It appears to us that Professor Kent's con- 

 tention is essentially this : that since the con- 

 cept of force is independent of quantity of 

 matter, distance and time, it is irrational to 

 force people to take their measure of force 

 from a dynamical equation involving these 

 three sorts of magnitudes. We should take 



