Since last letter, I have made some pairs of diagrams representing solid figures and curves drawn in space; of    these pictures one is seen with each eye by means of mirrors, thus . . .

This is Wheatstone's Stereoscope, which Sir David Brewster has taken up of late with much violence at the    Brightish Association. (The violence consists in making two lenses out of one by breaking it). (See Report). Last    winter he exhibited at the Scottish Society of Arts Calotype  pictures of the statue of Ariadne and the beast   seen from two stations, which, when viewed properly, appeared very solid.

 

 Since then I have been doing practical props on compression, and writing out the same that there may be no   mistake. The nicest cases are those of spheres and cylinders. I have got an expression for the hardness of a    cricket ball made of case and stuffing. I have also the equations for a spherical cavity in an infinite solid, and this   prop: Given that the polarised colour of any part of a cylinder of unannealed glass is equal to the square of the   distance from the centre (as determined by observation), to find—1st, the state of strain at each point; 2d, the
temperature of each.

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I have got an observation of the latitude just now with a saucer of treacle, but it is very windy.

Pray excuse this wickedly perplexed letter as an effect of the paucity of our communications. If you would sharpen   me a little it would be acceptable, but when there is nobody to speak to one [loses] the gift of speech. . . .