558 THE POPULAR SCIENCE MONTHLY. 



tain as complete a repose or refreshment of the mind upon some other 

 occupation as they can ; and they find that either after sleep, or after 

 some period of recreation by a variety of employment, just what they 

 want comes into their heads. A very curious example of this w r as 

 mentioned to me a few years ago by Mr. Wenham, a gentleman who 

 has devoted a great deal of time and attention to the improvement of 

 the microscope, and who is the inventor of that form of binocular mi- 

 croscope (by which we look with two eyes and obtain a stereoscopic 

 picture) which is in general use in this country. The original binocu- 

 lar microscope was made upon a plan which would suggest itself to 

 any optician. I shall not attempt to describe it to you, but it involved 

 the use of three prisms, giving a number of reflections ; and every one 

 of these reflections was attended with a certain loss of light and a cer- 

 tain liability to error. And, besides that, the instrument could only be 

 used as a binocular microscope. Now, Mr. Wenham thought it might 

 be possible to construct an instrument which would work with only 

 one prism, and that this prism could be withdrawn, and then we could 

 use the microscope for purposes to which the binocular microscope 

 could not be applied. He thought of this a great deal, but he could not 

 think of the form of prism which would do w T hat was required. He was 

 going into business as an engineer, and he put his microscopic studies 

 aside for more than a fortnight, attending only to his other w r ork, and 

 thinking nothing of his microscope. One evening after his day's work 

 w 7 as done, and while he was reading a stupid novel, as he assured me, 

 and was thinking nothing whatever of his microscope, the form of the 

 prism that should do this work flashed into his mind. He fetched his 

 mathematical instruments, drew a diagram of it, worked out the angles 

 which would be required, and the next morning he made his prism, 

 and found it answered perfectly well ; and upon that invention nearly 

 all the binocular microscopes made in this country have since been 

 constructed. 



I could tell you a number of anecdotes of this kind which would 

 show you how very important is this automatic working of our minds 

 this work which goes on without any more control or direction of the 

 Will, than when w y e are walking and engaged in a train of thought 

 which makes us unconscious of the movements of our legs. And I be- 

 lieve that in all these instances such as those I have named, and a 

 long series of others the result is owing to the mind being left to it- 

 self without the disturbance of any emotion. It was the w T orry which 

 the bank-manager had been going through, that really prevented the 

 mind from working with the steadiness and evenness that produced the 

 result. So in the case of the lawyer ; so in the case of the mathema- 

 tician ; they were all worrying themselves, and did not let their minds 

 have fair play. You have heard, I dare say, and those of you who are 

 horsemen may have had experience, that it is a very good thing some- 

 times, if you lose your way on horseback, to drop the reins on the 



