A CRITICISM. ii 



branches. I have taken some examples from Astronomy, which is con- 

 sidered the most exact of the physical sciences. Now does it not seem 

 curious that Astronomy the study of the heavenly bodies, which are the 

 most distant from us of all bodies, and most difficult to observe should 

 yet be the most perfect of the sciences ? Yet the reason is obvious. 

 Astronomy is the most perfect science because we know least about it be- 

 cause our ignorance of the actual phenomena is most profound. Situated 

 in fact as we are, on a speck in space, with our observations limited to 

 periods of time which, compared with the stupendous flights of the stars, 

 are merely momentary and evanescent, we are in somewhat the position 

 of a mole surveying a railway track and the flight of locomotives. And 

 as a man seeing a very small arc of a very vast circle easily mistakes it 

 for a straight line, so we are easily satisfied with cheap deductions and 

 solutions in Astronomy, which a more extended experience would cause 

 us to reject. The man may have a long way to go along his ' ' straight 

 line " before he discovers that it is a curve ; he may have much farther to 

 go along his curve before he discovers that it is not a circle ; and much 

 farther still to go before he finds out whether it is an ellipse or a spiral or 

 a parabola, or none of these ; yet what curve it is will make an enormous 

 difference in his ultimate destination. So with the astronomer ; and yet 

 Astronomy is allowed to pass as an exact science ! ' 



Well then, as in Astronomy we get an " exact science " because the 

 facts and phenomena are on such a tremendous scale that we only see a 

 minute portion of them just a few details so to speak and our ignorance 

 therefore allows us to dogmatise ; so at the other end of the scale in 

 Chemistry and Physics we get quasi exact sciences, because the facts and 

 phenomena are on such a minute scale that we overlook all the details and 

 see only certain general effects here and there. When a solution of cupric 

 sulphate is treated with ammonia a mass of flocculent green precipitate is 



i As another instance of the same thing, let me qnote a passage from Maxwell's 

 " Theory of Heat, " p. 31; the italics are mine : "In our description of the physical 

 properties of bodies as related to heat we have begun with solid bodies, as those which 

 we can most easily handle, and have gone on to liquids, which we can keep in open 

 vessels, and have now come to gases, which will escape from open vessels, and which are 

 generally invisible. This is the order which is most natural in our first study of these 

 different states. But as soon as we have been made familiar with the most prominent 

 features of these different conditions of matter, the most scientific course of study is in the 

 reverse order, beginning with gases, on account of the greater simplicity of their laws, 

 then advancing to liquids, the more complex laws of which are much more imperfectly 

 known, and concluding with the little that has been hitherto discovered about the con. 

 stitution of solid bodies." That is jto say that Science finds it easier to work among 

 gases which are invisible and which we can know little about than among solids, which 

 we are familiar with and which we can easily handle ! This seems a strange conclusion, 

 but it will be found to represent a common procedure of Science the truth probably 

 being that the laws of gases are not one whit simpler than the laws of liquids and solids, 

 but that on account of our knowing so much less about gases it is easier for us to feign 

 laws in their case than in the case of solids, and less easy for our errors to be detected. 



