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SCIENCE. 



[Vol. XXI. No 533 



branch of physics, but throughout the whole subject ; for train- 

 ing in making and reducing scientific observations; for acquir- 

 ing skill in manipulating and adjusting apparatus; all which is 

 to result in giving him a good general knowledge of physics, if 

 he follows the study no further, or to fit him for independent re- 

 search if such is his design for the future. It is thus intermedi- 

 ate in its thoroughness and definiteness between the preparation 

 in elementary general principles of the science, and the work of 

 the graduate or the advanced special student. 



What is likely to be the experience of a student in the college 

 laboratory under what we have called the progressive method, 

 supposing he has time enough in prospect to cover the entire 

 field? He will begin probably with a dozen companions in his 

 division, with the topic placed first in the order chosen, say 

 properties of matter, and dynamics. One of the first operations 

 he will be called upon to perform will be that of weighing a 

 body. The skillful use of a delicate balance, will involve the crit- 

 ical study of the balance itself. This will afford a good exercise 

 in dynamics. To reduce to weight in vacuo, will necessitate the 

 reading of the barometer, and an application of the laws of Boyle 

 and of Charles, for the effect of temperature and pressure upon 

 gases. Thus he will have been carried at once beyond the immedi- 

 ate subject of physics to which he was intending to apply himself. 

 However, it was merely an excm-sion. He may continue with 

 this work until he has learned several modes of weighing, and 

 with several types of apparatus. He must learn to measure 

 time. Here he will be introduced to the use of the pendulum, per- 

 haps the chronograph, and other devices for comparing intervals 

 of time. The method of coincidences will be especially service- 

 able, if he has a seconds clock and a reversible pendulum, by 

 which to determine the accelerative force of gravity. Atwood's 

 machine, besides illustrating the laws of falling bodies, will 

 serve for critical work in mechanics, if the effect of friction, and 

 the mass of the large pulley are to be considered. Various other 

 exercises in mechanics may be given him; he will hardly go on 

 with less than these, and to each of these he will have given 

 enough time and attention to become proficient in work of this 

 kind, and will have given attention to as little else in physics as 

 possible. 



If lie passes next to the subject of heat, he will probably 

 remain at this until he has dealt, if possible, as fully with 

 its various phenomena. So far as these phenomena involve me- 

 chanics he will have had some especial preparation by his previous 

 work, and now he will be doing that work over again. For in- 

 stance, in hygrometry the same principles relating to the effect of 

 temperature and pressure upon the volume of a gas, will have to 

 be considered. In specific heats, he will again go over the same 

 kind of work as to masses and densities that he performed with 

 the balance, and so on. But he will do nothing in electricity, 

 even with the heating effect of an electric current, because he 

 has not yet come to electricity. He will do heat pretty thoroughly 

 but not completely. It will be so in each branch he studies. In 

 every one, to do an exercise which is nominally one of a particu- 

 lar class, he must employ principles of classes previously studied. 

 Not until he has gone over the entire range of topics, from the 

 first to the last, will he have taken account of all the principles 

 meant to be included in his course, but when he has done so he 

 will have had a most exhaustive training, for he will then have 

 done nearly everything, not once or twice only, but very many 

 times. His training by that time ought to be excellent, and his 

 knowledge extensive and acute. But to reach such a stage 

 would require longer time or more exclusive devotion to physics 

 than is usually provided for in an undergraduate course. If any 

 thing less is done, however, it means not the omission of certain 

 exercises, but of all the exercises pertaining to one or another 

 entire class of topics. For instance, he may omit sound, or light, 

 wholly. That would make a serious break in his course. By 

 any of the usual arrangements, therefore, the whole subject will 

 be obviously more or less disjointed if it is regarded as made up 

 of members. Fortunately, the highest treatises seek to unify it 

 instead of to dismember it. 



How will the student fare by the method of analysis? For an 

 example, give him a piece of plate glass of convenient size. Of 



the various determinations regarding this specimen, some will be 

 qualitative, others quantitative. Let him determine: 



I. Whether it is regular, and if so, its form Qualitative 



3. Its dimensions, giving area, thickness and vol- 



ume Quantitative 



3 Its mass (weighing) Quantitative 



4. If c.G.s. units are employed, this leads at once 



by dividing mass by volume, to density Quantitative 



5. But check this by weighing in water, for sp. gr. Quantitative 



6. If the plate is of considerable size, say 25 cms. 



X 30 cms. and a small spherometer is availa- 

 ble, test the surface for flatness, and map out 



irregularities Quantitative 



(This will serve to show the meaning of instru- 

 mental limitations as to precision and ac- 

 . curacy) 



7. If possible, compare this with the irregularities 



of surface, shown by reflection of light, with 

 telescope, or by interference bands when in 

 contact with true ' ' flat." Qualitative 



8. Determine its index of refraction Quantitative 



9. Its hardness Qualitative 



10. Its color, by absorption in spectrum Qualitative 



II. Whether it is homogeneous, by transmission of 



polarized light Qualitative 



13. Its specific heat Quantitative 



Some of these may be out of the reach of many laboratory 

 equipments or only determinable with the help of instruments 

 too delicate to be put into the hands of any but the best students, 

 but still other determinations might be made. Undoubtedly by 

 the time the student has finished such an analysis he will have a 

 very complete knowledge of the specimen he has been working 

 upon, and although, in the instance here cited, the object under 

 scrutiny may seem a trivial one, and the knowledge of its prop- 

 erties no useful addition to his stock of information, not every 

 one may be so. Yet what a range of physics was involved even 

 in this apparently useless analysis ! In scientific training it will 

 not have been useless. 



As another example, suppose a steel rod be given him to ex- 

 amine. Cutting off a piece about 10 cms. in length, he might 

 determine its dimensions, mass, density, and specific heat. With 

 the long portion he can ascertain its rigidity (by torsion), Young's 

 modulus (by fiexure), velocity of sound in it (by longitudinal vi- 

 brations), and compare this with the velocity determined from 

 the ratio of elastioity to density. He might magnetize a short 

 piece, say 20 cms., by permanent magnets, and by timing its os 

 cillations, and observing the deflection it gives a needle, deter- 

 mine its magnetic moment, strength of pole, and strength of field 

 in which it swung. Let him then demagnetize it by heating, 

 remagnetize by electric current, and compare its moment now 

 with what it was before. These latter, though not properties of 

 the steel itself, are obtained as consequences of its magnetic char- 

 acter. He might also employ such a magnetized bar to deter- 

 mine its moment of inertia experimentally, and check by calcula- 

 tion from its mass and dimensions. Thus he will have brought 

 into application numerous principles of mechanics, of acoustics, 

 of heat and of magnetism, each of which gives opportunity for 

 work of any required degree of care and precision, involving all 

 the fundamental operations of weighing, measuring, and timing. 

 By the former method he will learn to what extent any one 

 quality is found in numerous specimens examined; by the latter, 

 to what extent these numerous and varied qualities aie found in 

 the one specimen examined; by the former he learns one feature 

 of many things, by the latter, many features of one thing. But 

 in learning the one feature he confines his attention chiefly to a 

 few principles of science and needs extend his knowledge of 

 physics no further than to apply these few principles, no matter 

 to how many objects, and there is always the danger of breaking 

 off his work with only a partial view of the science; whereas in 

 learning many features, thoughconfined to only one object, each 

 feature involves one or more distinct principles of science, and 

 the many of them represent a wide range of scientific knowledge. 

 This gives to the student, therefore, indeed it imposes upon him, 



