270 THE AMERICAN MONTHLY [November, 



those of diftVaction and interference, which were by no means 

 satisfactorily disposed of in Sir Isaac Newton's corpuscular h}'- 

 pothesis. The theory is that light is the vibrations of imponder- 

 able particles constituting the hypothetical ether, a substance 

 conceived as pervading all space and occupying the interstices of 

 all ponderable matter. 



Two of the phenomena of light demand particular attention — 

 refraction and diffraction. It is a matter of early observation 

 that light travels in straight lines. The dancing motes of dust 

 in the air, illuminated by the beam entering through some crevice 

 in the shutter, and the straightness of the beam, are familiar to 

 every child. Later it is noticed that objects partly immersed in 

 water seem to be bent at the water-line, and also that the coveted 

 pebbles in the brook lie much deeper than he had supposed. 

 These, with other phenomena of light, were illustrated by draw- 

 ings very carefully made, and full explanations of the laws de- 

 duced from them were given. It would not be possible to give 

 the explanations here without the diagrams, but all students of 

 physics are more or less familiar with them. 



The portion of Mr. Mitchell's paper of particular interest and 

 value to users of the microscope was in relation to angular aper- 

 ture in lenses. He said the question that led Professor Abbe to 

 his researches into the nature of microscopic vision was, "Why 

 does increased angles give objectives a greater resolving power.?" 

 Tlie results of this investigation were listened to with the keen- 

 est relish, and the discussion which followed showed that mem- 

 bers had given the matter considerable thought. At the conclu- 

 sion a cordial vote of thanks was tendered Mr. Mitchell. 



Auo?isi 77, i8g2. — This being a conversational meeting, no 

 business was transacted further than to arrange for a field day in 

 the near future, when those members who are interested will visit 

 the ponds, lagoons, and beaches in the vicinity of the city in 

 search of those minute forms of animal and vegetable life so inter- 

 esting to the enthusiastic microscopist. 



The paper presenteil was on the famous Santa Monica diato- 

 maceous deposit, carefully prepared and read by Henry C. Hyde. 

 The paper gave a brief account of the finding of this fragment by 

 Thomas P. Woodward, now a school director in this city, but in 

 1S76 connected with the United States Coast Survey. The gen- 

 tleman was present as a visitor to the society, and gave a brief 

 account in corroboration of what was read. 



The fragment was a little larger than the dimensions of a long 

 cigar box, and a portion was broken ofi' to admit it into the box for 

 shipment to this city, where it was sent to Henry G. Hanks, then 

 in charge of the State Mining Bureau. An examination by Mr. 

 Hanks at once revealed its character, but as he was not specially 

 interested in diatoms, the bulk of the specimen was turned over to 

 Professor Ashburner, who sent portions to various persons in the 

 United States and in Europe who were interested in the subject. 



