X. 



ON CHEMICAL RATS AND THE STRUCTURE AND 

 LIGHT OF THE SKY. 



The first physical investigation of any importance in 

 which, jointly with my friend Professor Knoblauch, I took 

 part, bore the title : " The Magneto-optic Properties of 

 Crystals, and the Relation of Magnetism and Diamagnetism 

 to Molecular Arrangement." 1 This investigation compelled 

 me to reflect upon the structure of crystals, on their optical 

 properties in relation to that structure, and more particu- 

 larly on the striking phenomena exhibited by many of 

 them in the field of a sufficiently powerful magnet. These 

 were evidently due to the manner in which the molecules 

 of the crystals were built together by the force of crystal- 

 lization ; and it was natural, if not necessary for me, to em- 

 ploy such strength of imagination as I possessed in obtain- 

 ing a mental picture of this molecular architecture. The 

 inquiry gave a tinge and bias to my subsequent scientific 

 thought, rendering, as it did, the conceptions and pursuits 

 of molecular physics pleasant to me. Its influence is to be 

 traced in most of my scientific work. The first lecture, for 

 example, which I ever delivered in this theatre, was " On 

 the Influence of Material A^oTeffation on the Manifestations 

 of Force ; " by " material aggregation " being meant the 

 way in which, by Nature or by Art, the molecules of mat- 



1 Philosophical Magazine, July, 1850. 



