i2o THE POPULAR SCIENCE MONTHLY 



physics, has to do with those phenomena of the atmosphere, the ocean, 

 or the magnetic state of the earth, which are not controllable by man, 

 and which can not, therefore, be repeated at pleasure in the laboratory, 

 but must be observed when and where they occur. The same applies 

 to geology, which is the ajDplication of physics, chemistry and even 

 biology, or any science whatever, to the earth, in relation to its physical 

 constitution and its history. Geography deals with the face of the 

 earth, and uses the results of geology to study the earth as fit to be the 

 dwelling place for man. There remain the technical applications of 

 physics in all kinds of engineering, civil, mechanical, electrical, chem- 

 ical or mining, involving the strength of materials, elasticity and the 

 direction of the natural sources of energy to the purposes of man. 

 All these applications of physics need, and are highly susceptible to, 

 mathematical treatment, and for that reason they are the most perfectly 

 developed of all the sciences. 



Let us now turn to the biological sciences. The two fundamental 

 divisions, zoology and botany, dealing with animals and plants, seem 

 to run continuously one into the other, like chemistry and physics. 

 Under both we have the subdivisions of morphology for the study of 

 form and physiology for function. Under zoology we put anatomy, 

 and the various more specialized sciences which find their technical 

 application in medicine. There still remain anthropology, the study 

 of man and his practises, psychology, which deals with the workings 

 of what we call his mind, or that of animals, sociology, properly a part 

 of anthropology, dealing with man when living with his fellows, and 

 economics striving to teach him how to get along with them still better. 



This classification is admittedly rough, but it does not separate 

 closely connected things as some that I have seen do. For those who 

 desire finer splitting I refer to the classification of the Scientific Con- 

 gresses of St. Louis in 1904. Of these biological sciences the methods 

 are somewhat different, they are mostly still in the descriptive stage, 

 and have rarely attained sufficient quantitative information to be 

 capable of mathematical treatment. And yet that must be their ulti- 

 mate object, for without mathematics there is no exact description. 

 That this is not impossible even in biology may be seen from the 

 following example. If a bacterial culture be inoculated into a jelly 

 with the point of a needle, it will be seen under the microscope to 

 grow in all directions from the original center, and if pains are taken to 

 ensure the physical homogeneity of the jelly the shape of the colony will 

 be an almost perfect circle. If the diameter of this circle be measured 

 at regular intervals, I have no doubt that a quantitative law of growth 

 can be deduced, and even a differential equation found, which will turn 

 out to resemble that of certain physical phenomena, say the conduction 

 of heat. We may observe that the instruments and methods of the physi- 



