Balh Literary and Philosophical Society. 297 



very weak state, and slowly left its original abode. The rapidity 

 with which tlie insect enlarges after this, i^ surprising ; in the 

 course of a few hours it can fly to the top of the tallest eucaly- 

 ptus, whicli u;eiierally grows to the height of sixty or seventy feet. 

 On this tree Colonel Pateison first discovered the mam. a in great 

 quantities, apparently produced bv these insects It may be col- 

 lected l)oth in a liquid and in a saccharine state : the inhabi- 

 tants gathered it, and used it for some time as sugar, but soon 

 discovered that it possessed in some degree the quality of manna. 

 The extraordinary noise these little creatures make is deserving 

 of notice : the males first begin with a note similar to that of 

 the land-rail, and repeat it for several times ; at length the fe- 

 males join, when the combination of notes exactly resembles the 

 noise of grinding knives or razors ; and hence tlie insect is po- 

 pularly known by the name of the razor-grinder. It makes its 

 appearance about the end of November, and early in January de- 

 posits its eggs in the ground. The larva is perfect in September, 

 when it is formed into the pupa, in which state it remains until 

 November. There is a species of the insect in New South Wales 

 of the same appearance, and which makes the same sort of noise, 

 but produces no manna. 



Mr. Eckersall observed that the locust, when used as food, 

 contracts the usual period of life, and induces that cutaneous 

 aflfection of winged insects generated on the surface of the body, 

 producing universal ulceration. 



Dr. Wilkinson stateti that he had received a letter from Mr, 

 Bakewell the geologist, communicating that, from some obset- 

 vations on basaltic formations, he was led to believe that the 

 basalt makes its appearance at Wick and dips imder Bath, 

 where it has some connexion with the production of the warm 

 springs. 



The Society proceeded to the consideration of a paper for- 

 merly presented by Dr. Wollaston relative to th.e theory of the 

 diamond cutting glass. It was stated by Dr. Woihiston, that the 

 natin-al point of the diamond answered better than an artificial 

 point ; and that, in cutting glass, the line described is a tangent 

 to the face of the diamond. Dr. Wilkinson mentioned that he 

 had some micrometers made by the late Mr. Coventrv, where the 

 lines on glass had been so finely drawn, that the cross lines formed 

 a series of squares so minute that twentv-five millions of squares 

 are only equal to o:ic ••<iu:ue inc-h. Dr. W. observed, that when 

 a glass is cut properly by a diamond, the line of section has a very 

 diflferent appearance from a line drawn by an improper inclina- 

 tion of the point; the particular difference he promised to state 

 at a future meeting. It was conjectured by one of the members, 

 that the effect of the action of the diamond may not be a me- 

 chanical 



