CHAP. V.] OPENING MANHOOD 1847 TO 1850. 123 



[Herefolloiv thirteen diagrams of patterns in triangles, squares, 

 pentagons, and hexagons] These are a few of the figures one 

 sees in unannealed glass. 



Pray write soon and tell when, how, and where by, you 

 intend to come, that you may neither on the other hand fall 

 upon us at unawares, nor on the one hand break and not 

 come at all. I suppose when you come I will have to give 

 up all my things of my own devizing, and take Poisson, for 

 the time is short, and I am very nearly unprepared in actual 

 reading, though a great deal more able to read it. 



I hope not to write any more letters till you come. I 

 seal with an electrotype of the young of the ephemera. So, 

 sir, I was, etc. 



To THE SAME. 



Bannavie, 6th July [1849'}. 



This being a wet night, and I having exhausted my 

 travelling props, set to to write to you about what I can & 18. 

 recollect of my past history. It is curious that though the 

 remembrance of ploys remains longer than that of home 

 doings, it is not so easily imagined after a short interval. 



By imagining is here meant bringing up an accurate 

 image of thoughts, words, and works, and not a mere 

 geographical summary of voyages and travels. 



But to the point. Perhaps you remember going with 

 my Uncle John Cay (7th Class), to visit Mr. Mcol in 

 Inverleith Terrace. There we saw polarised light in abun- 

 dance. I purposed going this session but was prevented. 

 Well, sir, I received from the aforesaid Mr. Cay a "Mcol's 

 prism," which Mcol had made and sent him. It is made 

 of calc-spar, so arranged as to separate the ordinary from the 

 extraordinary ray. So I adapted it to a camera lucida, and 

 made charts of the strains in unannealed glass. 



I have set up the machine for showing the rings in 

 crystals, which I planned during your visit last year. It 

 answers very well. I also made some experiments on com- 

 pressed jellies in illustration of my props on that subject 

 The principal one was this : The jelly is poured while hot 



