2 3 8 



SCIENCE. 



ON SOME NEEDED CHANGES AND ADDITIONS 

 TO PHYSICAL NOMENCLATURE. 



By Professor A. E. Dolbear. 

 I. — Physics is now defined to be the science of 

 energy. Previous to 1840 what was known concern- 

 ing energy was embodied in Newton's Laws of Motion, 

 and was confined to what we may call molar mechan- 

 ics, to distinguish it from atomic and molecular me- 

 chanics, which has since that time been developed. 

 Friction was looked upon as resulting in an absolute 

 loss of energy, and no attempt appears to have been 

 made to find it in other forms. Both Rumford and 

 Davy proved, to their own satisfaction, that friction re- 

 sulted in the creation of heat — an idea entirely differ- 

 ent from the conception of heat then in vogue, that it 

 consisted in imponderable corpuscles. No attempt 

 was made to find the quantitative relation between 

 molar energy expended and the heat produced, so 

 that many years elapsed before any advance was made 

 beyond the qualitative work of Rumford and Davy. 

 Even for a time after Faraday's researches had estab- 

 lished a quantitative relation between chemical reac- 

 tions and electricity, the facts were looked upon as 

 rather curious information, out of relation with physics 

 proper, and so the latter was kept strictly what is in- 

 volved in 



T^ -r^ III ifi. 



Energy E = - 



2 



the form of the energy being modified by so-called 

 " Mechanical Powers," the lever, the pulley, the in- 

 clined plane, etc. Since 1840, however, through the 

 labors of Mayer, Joule, Thomson and others, the 

 quantitative relations between the various known 

 forms of energy have been determined with great pre- 

 cision, and has led to a complete and inclusive gener- 

 alization of the laws of energy — namely, that the 

 energy in the universe is a constant quantity, the form 

 that it may assume at a given time and place depend- 

 ing solely upon the other forms of energy which are 

 present at the same place at that time. By the form 

 of energy is meant the character of the motion thai em- 

 bodies the energy, for when there is no motion there is 

 no energy, so that each different form of motion is a 

 different form of energy. Rectilinear motion is a dif- 

 ferent form from rotatory motion, inasmuch as in rec- 

 tilinear motion there is a change of position in space 

 of the centre of mass, while rotatory motion does not 

 involve such change, yet both embody energy though 

 each in a special form and each should have a specific 

 name. 



Generically, all motion of translation in space is 

 called mechanical motion or molar motion, and its 

 energy, oni I its vis viva, is proportional to 



m ;■■ 



. and is true for masses ol all dimensions. 



E = 



m v 

 2 



Nevertheless, what a given amount of energy will do 

 depends solely upon its form. Rectilinear motion 

 cannot continuously produce rotatory motion ; but 

 vibratory motion can. For convenience in descrip- 

 tive work as well as for clearness of conception — the 

 latter of great importance — it is necessary to have 

 specific names for the various forms of energy. As 

 each form embodies a particular form of motion, one 

 will only need to specify the various possible forms of 

 motion in order to cover all possible cases. We have 

 then the following table for such mechanical or molar 

 motions : 



Rectilinear, like a locomotive upon a straight 



track 

 Rotatory, like that of a balance wheel. 

 Vibratory, like that of a tuning fork. 

 Curvilinear, like that of a projected cannon 



ball. 

 Spiral (unusual), like some forms of projected 



rockets. 

 Vortical, like smoke rings. 



As the energy of each of these forms is expressed 

 by the same formula there is no way of identifying 

 either of them, except by some roundabout expression 

 as " The energy of vibration," " The energy of curv- 

 ilinear motion." It is true that for one of these 

 forms we have a particular name, sound, for vibratory 

 motion, provided its frequency is within the limits of 

 hearing, but as the same name is applied to the sen- 

 sation itself we are without a distinctive name. 



II. If instead of large masses we consider atoms and 

 molecules, it will be clear at once that the same forms 

 of motions are possible as with the large masses, and 

 the same general descriptive terms are applica- 

 ble. Thus for an atom there is a rectilinear motion 

 which we call its free path, but for its vibratory motion 

 we use a distinct and and specific name, heat. Also 

 for the rotation of the atom in its own plane, we have 

 the specific name, electricity; for possible curvilinear 

 spiral or vortical motions there are no names. 



The energy embodied in atomic and molecular 

 motions exclusive of rectilinear, that is, that do not 

 involve a change of position of the centre of mass or 

 of inertia of such atom is generally called internal 

 energy, and if we let e represent its value then the 

 complete expression for the energy of the atom will be 



T,, 111 7' 2 . 



E = e 



2 



Now such changes and conditions as are involved 

 in what we call latent heat, specific heat and specific in- 

 ductive capacity are all involved in that factor e, but 

 the terms specific heat and latent heat are certainly 

 misapplied, for whatever the forms of energy may be, 

 they are certainly not heat, consequently not vibratory. 

 Specific names then arc needed for these. 



III. The observed transferrence of energy from one 

 atom to another without contact has necessitated the 



