1854.] 



LECTURE BY JOHN LANGTON ESQ., M.P.P. 



203 



Watt was not only a skillful mechanic, but thoroughly conversant with 

 most of the sciences ; and in our own time Scott Russell, who, by a 

 series of beautiful and most ingenious experiments, was the first to 

 demonstrate the true form of vessels offering the least resistance to the 

 water, has become himself an eminent shipbuilder. Even in these 

 branches of study which are in themselves of a less practical charac- 

 ter, the assistance of instruments, and various complicated mechanical 

 contrivances, is constantly required, and the investigator must be able 

 to devise and direct, even if he does not himself actually construct 

 them. The ingenious instruments invented by the late Dr. Wollaston, 

 and by Professor Wheatstone, are instances of this union in a high 

 degree of mechanical skill and theoretical acuteness. Newton made 

 with his own hands most of the instruments with which his delicate 

 optical experiments were conducted, and he invented, and himself con- 

 structed, the kind of reflecting telescope which bears his name ; and after 

 him Herschel and LordRosse manufactured themselves those great in- 

 struments which have given us a new insight into the heavens. 



In these remarks I do not merely confine myself to advocating a scien- 

 tific training for mechanics, as a means of enabling them to pursue their 

 several callings with greater success ; I go a step farther, and recom- 

 mend it for the sake of science itself. 'With similar advantages of scien- 

 tific acquirements, a working mechanic is more likely than any other 

 person to strike out something new and useful in practice, or something 

 important in principle. He has the best opportunities of perceiving 

 what is deficient in the existing state of his art, and what is the chief 

 difficulty to be overcome. He is daily handling the tools and materials 

 of his trade, and assisting in processes and operations upon a scale and 

 under circumstances which the experimenter in his cabinet cannot imi- 

 tate. Indications of the secrets of nature are constantly passing under 

 his eyes of which the mere philosopher can know nothing. Yet all 

 these advantages must be barren and useless, unless some knowledge 

 of principles and a habit of generalizing enable him to seize the liint, 

 and turn it to account. The seed is being liberally scattered, but un- 

 less the soil is prepared for its reception, it will bring forth no fruit. 



It is not often that we know with any certainty the whole history of 

 a new discovery, but when we do, we very generally find that it origi- 

 nated in a trifling indication such as I have spoken of, which hundreds 

 of people had seen before, without thinking it worthy of attention. Even 

 when the discovery is the result of a laborious investigation for that 

 especial object, the original inducement to commence the inquiry has 

 often been some casual observation, or the final course of reasoning 

 which has led to its success has been dictated by an accident, which 

 has caused the whole mystery to flash across the mind in an instant. 

 Such discoveries are frequently spoken of as accidental, and if they 

 are so, such chances are more likely to occur to practical men than to 

 any others ; but to call them accidents has a tendency to mislead, and 

 at any rate does not tell the whole truth. Such chances occur daily 

 to tir all, but it is only the favored few that can take advantage of 

 them. When a man's mind is deeply intent upon some particular sub- 

 ject, a mere trifle may often give it an impulse which leads to a new 

 view of the question, and ultimately to a new discovery ; but the bent 

 of the mind must already exist, and the capacity to turn the new idea 

 to advantage. 



It may be interesting to illustrate this by some examples. 



The story of Archimedes is well known. Hiero, King of Syracuse, 

 had given a certain weight of gold to a jeweller, from which to manu- 

 facture a crown ; and when the crown was brought to him, and found 

 to be of full weight, he still wanted to know whether it was all really 

 gold, or whether the weight had been made up with baser metal, and 

 he consulted Archimedes. The question, evidently, was to determine 

 whether the bulk of the manufactured crown was the same as that of 

 the gold given out ; for, if it were no greater, gold being the heaviest 

 metal then known, it would be clear that it must be all pure gold. 

 Whilst meditating upon this commission, Archimedes went into a bath, 

 and noticed how his body, by displacing a quantity of water equal to 

 its bulk, raised the level of the whole, as if a similar amount of water 

 had been added. The whole secret was seen through in a moment, 

 and he is said to have jumped out of the bath, and to have run home, 

 forgetting even to dress himself, and exclaiming, as he went, that he 

 had found it out. This is a fair specimen of these accidental discove- 

 ries. Thousands had seen the water rise in a bath before, but it was 

 only to a man of the attainments of Arcliimedes — and he, too, in search 

 of the hint he found — that the accident gave rise to the discovery of 

 the hydrostatic balance, of specific gravities, and the whole theory of 

 floating bodies. 



It was more purely an accident when Hauy dropped a beautiful crys- 



tal, which he was examining, on a marble floor, and, on gathering up the 

 fragments into which it was shivered, discovered that crystals have 

 planes of cleavage differing from their outward forms, and thus created 

 an entire change in that branch of mineralogy, Substances which 

 crystalize, always assume certain definite forms by whieh they may 

 generally be recognized; but most crystals are subjeet to great modifi- 

 cations of figure, and some so much so, that they lose even a general 

 resemblance to their usual characteristics. Thus, suppose a common 

 brick to be the primary form in which a substance crystalizes : as fresh 

 additions are made, the whole mass may still keep the shape of the 

 first brick ; but from the same materials you may also build up a square 

 tower, or a pyramid. The outward form does not, therefore, neces- 

 sarily exhibit the interior arrangement of the separate parts ; but if 

 you can obtain planes of cleavage, which show the courses of masonry, 

 and the direction of the joints, you can detect the original brick, whether 

 in the pyramid or the tower. This was the nature of Hauy's discovery, 

 arising from a mere accident; but the occurrence would have been 

 fruitless to any but an accomplished mineralogist, who had already 

 directed his attention to the forms of crystalization. 



Again : it was by accident that a French officer of engineers, named 

 Malus, was looking at the reflection of the setting sun on the windows 

 of the Luxemburg Palace, through a plate of doubly-refracting crys- 

 tal, called tourmaline, when he remarked that one of the images dis- 

 appeared on turning the crystal round. Hundreds might have seen 

 the same tiling, but it was only in the case of one already engaged in 

 the study of optical phenomena that the observation gave rise to a 

 most singular and important discovery, that, when reflected or refracted 

 in a certain manner, light attains an entirely new property, and ever 

 after refuses to be reflected or refracted except in certain directions. 

 Light thus modified in its nature, so as to have a definite relation to 

 space, and to affect certain directions in preference to others, is said 

 to be polarized, from a sort of analogy with the magnetic needle, whereas 

 common light traverses transparent bodies in any direction, being only 

 reflected or refracted at their surfaces. When thus changed in charac- 

 ter, it meets with somewhat similar obstructions in their interior, giv- 

 ing rise to some most singular and splendid displays of colour, and, 

 what is more important, giving us a deeper insight into the internal 

 constitution of matter than was ever attained before, and we are appa- 

 rently as yet only on the threshold of the discoveries it may lay open 

 to us. 



It is related of Galileo, that, whilst attending divine service in the 

 cathedral at Pisa, he noticed that a chandelier, which had in some way 

 been disturbed, continued to swing in exactly equal intervals of time. 

 No accurate measure of time was known in those days, so he tested 

 the quality of the vibrations by his own pulse. As he was at that time 

 studying for the medical profession, he employed his discovery in a 

 little instrument for counting the pulse of his patients. Afterwards, 

 when he deserted medicine for the physical sciences, he founded upon 

 it many of his new, but just views of the laws of motion ; and in later 

 life, when he became an astronomer, the same accidental observation 

 supplied him with the pendulum for his clock. Such occurrences can- 

 not fairly be called accidents. Almost every living man from the com- 

 mencement of the world must have seen something similar, but it re- 

 quired a Galileo to detect its value, and to trace its important conse- 

 quences. 



In the following century, the astronomer Bradley was engaged in a 

 series of observations on the stars, intended to obtain a decisive proof 

 of the motion of the earth from the known principle of parallax, when, 

 instead of what he was looking for, he observed another, and to him 

 unaccountable, apparent motion of the stars. He had long endeavoured 

 to find some solution of the difficulty, and his mind, no doubt, was full 

 of it at the time, when, in sailing in a boat on the Thames, he noticed 

 that the vane at the mast-head was directed to a different point of the 

 compass at each tack the boat made, though the wind itself had in no 

 respect changed. In fact, a vane under these circumstances, being 

 partly acted on by the wind, and partly by the motion of the boat itself 

 through the air, assumes a position intermediate between the two direc- 

 tions. It immediately struck Bradley that his observed motion of the 

 stars might be similarly accounted for ; that the ray of light, the direc- 

 tion of which he had been measuring with his telescope, might be com- 

 pounded of the real direction in which it was moving from the star, 

 and of the direction which the earth itself was advancing at the time ; 

 so that, as the earth kept changing its direction in different parts of 

 its orbit, the apparent direction of the star would vary just as that of 

 the vane did. This supposition he was afterwards fully able to verify, 

 and it forms to the present day, or till within the last few years, at any 



