22 



SCIENCE. 



[Vol. XX. No. 492 



well, each evolves a dynamical or mechanical theory of light, 

 a lack of agreement among them or with known principles 

 of optics can generally be traced to the fact that the medium 

 in which they suppose the action to take place has not been 

 endowed with the same common properties by all, and that 

 in every case it falls short of an exact representation of the 

 real ether itself. With this important restriction upon 

 mathematical reasoning kept continually in mind, mathe- 

 matics may be safely set aside as the "one science of pre- 

 cision." 



What, now, are the characteristics of the so-called "exact 

 sciences " other than pure mathematics ? Without attempt- 

 ing a rigorous deSnition or a precise classification, it is suffi- 

 cient for the purpose at hand to declare that the exact sci- 

 ences are those whose conclusions are capable of being, and 

 for the most part are, established by experiment and verified 

 prediction. 



Among these exact sciences the most notable, in degree of 

 exactness, is the science of astronomy. Although the con- 

 clusions reached in the study of astronomy may not in gen- 

 eral be established by experiment, the marvellous accuracy 

 with which its predictions are verified has long ago placed 

 it far in advance of other sciences. An inquiry into the 

 cause of this excellence will not show that the logic of the 

 astronomer is any more rigorous than that of many others 

 engaged in scientific research, but rather that the premises 

 on which he reasons are simpler, and, what is of greater im- 

 portance, more nearly sufficient. Until a very recent period 

 in its history, astronomy, although dealing with matter, has 

 been concerned almost entirely with only one of its many 

 properties. The one property thus far assumed to be com- 

 mon to all matter is that long-known but still mysterious 

 attraction in virtue of which there exists a stress between 

 every particle and every other particle in the universe, ac- 

 cording to a law the discovery and exposition of which justly 

 entitles Newton to be considered the greatest philosopher of 

 all ages. It happens that the hundreds and possibly thous- 

 ands of other properties possessed by, or inherent in, matter 

 have little if any influence on the dynamics of masses widely 

 separated from each other, and therefore a knowledge of the 

 law of gravitation seems to be sufficient to enable the astron- 

 omer, having, of course, obtained the necessary data from 

 observation, to trace the paths of the planets and to foretell 

 the configuration of the heavens many years in advance. 

 Within the past twenty-five years, however, the splendid 

 discovery of spectroscopy, aided by great improvements in 

 photography, has given rise to a new astronomy, known as 

 physical, as distinguished from gravitational astronomy. 

 The new science deals with a matter of many properties, 

 some of which are but little understood While its conclu- 

 sions are of vital importance and of intense interest, they 

 result from deductions in which the premises are insuflicient 

 and are proportionately uncertain. The new astronomy 

 must for a long time abound in contradictions and contro- 

 ■yersies, until, and largely through its development, we shall 

 possess a knowledge of the properties of matter when sub- 

 jected to conditions differing enormously from those with 

 which we are now quite familiar. Because one astronomer 

 declares that the temperature of the sun is 20,000° F., and 

 another, equally honest and capable, says it is not less than 

 20,000,000° F., it must not be inferred, and it never is, except 

 hy the superficial, that the whole science of solar energy is a 

 tissue of falsehoods, and that those engaged in its development 

 are deliberately planning an imposition upon the general 

 public. Even such widely varying results as these may be 



based on observations that are entirely correct and experi- 

 ments that are beyond criticism. The discussion of the re- 

 sults obtained by observation and experiment may follow, in 

 both cases, the very best models, and yet the conclusions may 

 be erroneous and contradictory, owing to the insufficiency of 

 data in the beginning. 



Unfortunately the omission of one or more important 

 quantities from the equations of condition is not always 

 known or suspected. The older, more exact astronomy is 

 occasionally caught tripping in this way. An interesting 

 example of recent occurrence is to be found in certain ob- 

 servations for stellar parallax made a few years ago by 

 members of our own society. The observations were long 

 continued, the instruments used were of a high character, and 

 the observers were skilful. These conditions unquestionably 

 promise success. It was something of a surprise, therefore, 

 when a reduction of the observations gave for the parallax 

 a negative result. As such a result could in no way be pos- 

 sible, except, perhaps, through the assistance and interven- 

 tion of a curvature in space (in virtue of which if a man's 

 vision was not limited he would, by looking straight for- 

 ward, see the back of his own head), it was assumed that the 

 work was not as well done as it seemed to be, or that some 

 imperfection in the instrumental appliances had been over- 

 looked. It now appears, however, that this record may be 

 reopened, and that the results may prove to be of as great 

 value as originally anticipated. Researches carried on dur- 

 ing the past year or two have with little doubt established 

 the fact that the latitude of a point on the earth's surface is 

 not a fixed quantity, but that on the contrary it varies through 

 a small range during a period somewhat greater than a year. 

 It is believed that if this hitherto unsuspected variation be 

 applied to the parallax observations, referred to above, the 

 seeming absurdity of the result will vanish. 



If astronomy, the foremost of the exact sciences, is not 

 free from the fault of basing conclusions upon insufficient 

 premises, it will not be expected that among other sciences 

 the evil will be of less magnitude. 



When we consider the sciences of heat, light, electricity, 

 magnetism, and other specially investigated properties of 

 matter, all of which are usually included under the general 

 head of "Physics," we meet with a formidable rival of as- 

 tronomy in the extent to wbich they are entitled to be con- 

 sidered as exact sciences. 



Physics treats of all the properties of matter, not omitting 

 that which is the special domain of astronomy. As if this 

 were not enough, the demands upon the science are such that 

 it must also deal with that which is not matter, or, at least, 

 is not matter in the ordinarily accepted sense. Although 

 physics deals with all of the properties of matter, no physi- 

 cist knows them, or, possibly, half of them. Perhaps not 

 one of them is entirely and completely known. It would 

 seem, therefore, that this science must of necessity be one of 

 uncertain conclusions. That it is far from deserving so 

 sweeping a criticism is due to the fact that the properties of 

 matter are not so closely interrelated as to make it impossi- 

 ble to isolate one or more of them in experiment, and thus 

 the problem is vastly simplified. It is probably impossible 

 to do this rigorously in any case, so that there must always 

 remain a small residuum of jincertainty due to the interfer- 

 ence of unknown or imperfectly understood properties of 

 matter. 



Thus it is possible to treat a mass of matter as though it 

 possessed mass only, ignoring its electrical, magnetic, or 

 optical properties, its relation to heat, its elasticity, and other 



