222 



Pyrites on the 

 shore at Har- 

 wich. 



Seawater ap- 

 pears to assist 

 in its fonnati- 

 on, converting 

 wood, &c. into 

 pyrites. 



ON GRAVITATION. 



When I was in London 5'ou may perhaps recollect I men- 

 tioned to you, that considerable quantities of iron pyrites 

 were to be found upon the sea shore at Harwich. I have 

 embraced the present opportunity of sending you a small 

 specimen for your inspection. It would be curious to as- 

 certain the true theory of its formation. From the little 

 observation I have had an opportunity of making, 1 am per- 

 suaded its formation is considerably aided by the seawater. 

 Pieces of wood, bone, &c. become converted into it by time, 

 and lose every trait of their origin, except the shape of the 

 grain, which in many specimens is nicely preserved. The cliff 

 above the shore appears to be almost entirely composed of a 

 blueish soft clay, which is continually crumbling and falling 

 down upon the beaclj, and is washed by the waves, and I 

 think a curious obocrver conversant in mineralogy might 

 easily trace the formation of the pyrites by gradation from 

 the clay, as pieces may be found in several different states, 

 and it appears to he influenced by the alternate action of 

 the air and sea water, but in what way I am entirely at a 

 loss at present to conjecture. 



Jpsuich, 6th of June, 1 808. 



Two mistate* 

 jncnts in the 

 last le ter of 

 Dytiscus. 



XII. 



Letter from Professor Vince, in Reply to Dytiscus. 



To Mr. NICHOLSON, 



SIR, 



JL Shall esteem it a favour, if you will insert a few remarks 

 on the observations of Dytiscus in your last Journal, en- 

 gaging not to trouble you again on this subject. 



In the first paragraph there are two unaccountable misre- 

 presentations, for I would not charge Dytiscus with doing 

 it wilfully. He says, " the two first terms of the series very 

 possibly allude to the two first terms of the only two series 

 which are to be found in the essay, these two terms having 

 been already mentioned as sufficient for determining the 

 force" Now I have put down the first terms of three of 



the 



