Mr. Batchelor on Musca Volitantes in the Eye. \ 65 



Dry clay 12 



Flint, black 11, 30 



Portland stone, hard 14 



Quartz, white 56 



Blue pebble, like Rowley rag 105, 110 



Coarse limestone, near Stilton, Huntingdonshire 60 



Gritstone on road, near Leeds 100, 115 



Yorkshire paving-stone 20 



Ketton, hard 20 



Tetternhoe 4 



Chert f?] from hills in Devonshire and Cornwall 57 



Gray wether of Hertfordshire and Wiltshire .... 18 



Grit of upper bed, Colly weston, near Stamford, 



Lincolnshire 40 



Second bed, do 100 



Slate at do 50 



Stockton limestone, Warwickshire, (lias) 45 



Newbold-on-Avon do 36 



Limestone of Stoke Cruerne, Northamptonshire 35 



The steady pressure, without percussion, required to crush 

 a piece of the marble weighing \ oz. = 600 Ibs. 



To crush the gray flint of 1 -2 oz. weight = 2000 Ibs. 



To crush rolled white quartz pebble 2 oz. = 3400 Ibs. 



B.B. 



P.S. To-day we have summer weather. At half-past three 

 this morning, in clear starlight, the exposed thermometer 



was at 48 



At half-past seven in the morning 49 



At half-past one in the day 60 



At half-past five this afternoon 54 



The larks and other spring birds are singing; and the 

 yellow butterfly is in full action. B. B. 



Leighton Bussard, Feb. 10th, 1831. 



XXIX. Observations on a Species of Muscce Volitantes appa- 

 rently existing in the Aqueous Humour of the Eye. By 

 THOMAS BATCHELOR, Esq.* 



AMONG the numerous defects and diseases to which the 

 component parts of the eye are subject, accidental cir- 

 cumstances have led me to investigate several, which appear 

 to have their seat in the humours ; and which, as far as 1 can 

 learn by inquiries among medical men, are not very accurately 

 understood. That disorder of vision, to which I shall chiefly 



* Communicated by the Author. 



confine 



