TO C. J. MONRO, Esq.

                                                                              Glenlair, Springholm, 
                                                                           Dumfries, 20th May 1857. 

I went to Old Aberdeen for Fourier,  . . but I have forgotten what was to be discovered out of him. 

The session went off smoothly enough. I had Sun all the beginning of optics, and worked off all the experimental    part up to Fraunhofer's lines, which were glorious to see with a water prism I have set up in the form of a cubical   box, 5 inch side. The only things not generally done that I attempted last session were the undulatory medium   made of bullets for advanced class, and Plateau's experiments on a sphere of oil in a mixture of spirits and water  of exactly its own density. 

     I succeeded very well with heat. The experiments on latent heat came out very accurate. That was my part, and  the class could explain and work out the results better than I expected. Next year I intend to mix experimental     physics with mechanics, devoting Tuesday and THURSDAY  (what would Stokes say?) to the science of    experimenting accurately. 

     I got a glorified top made at Aberdeen. I think you saw the wooden type at Cambridge. I have made it the occasion of a short screed on rotation coming out in the Roy. Soc., Edinburgh, presently. 

     Last week I brewed chlorophyll (as the chemists word it), a green liquor, which turns the invisible light red. My    pot of all the winter spinach that remained was portentous, so I exhibited the optical effects, which were allowed   to be worth the potful. 

     My last grind was the reduction of equations of colour which I made last year. The result was eminently    satisfactory.