Nutmegs. — Optical Illusion. 397 



consists of a number of fibres issuing from the stalk, and 

 its continuation through the centre of the fruit, the other 

 ends of which fibres, though closely surrounded and pressed 

 by the fruit, do not adhere to it ; the consequence is, that 

 when the stalk is grated away, those fibres having lost their 

 hold, they insenstbly drop out, and the nutmeg appears 

 hollow ; and as more of the stalk is grated away, others of 

 them drop out in succession, and the hollow continues 

 throuah the whole nut ; whereas by beginning to grate at 

 the odier end, the fibres above mentioned are grated off at 

 their core end with the surrounding fruit, and they do not 

 drop out a,nd cause a hole. The want of knowing this has 

 caused many excellent nutmegs to be condemned as da- 

 macred fruit, and others, of perhaps less value, to be com- 

 mended, according as accident or caprice caused them to 

 be grated from the stalk, or top enA. And here I beg tp 

 mention, that, the oil of nutmegs being of great value, it 

 has often been extracted from the nuts which are exposed 

 to sale, whereby they are rendered of very little value ; and 

 the way to knovv good nutmegs is to force a pin into them, 

 when, if good, however dry they may appear, the oil will 

 be seen to ooze out all round the pin, by the compression 

 occasioned in the surrounding pans by its being forced in. 



F. 



To Mr. Tilloch. 

 Sir, — Having lately, sometimes, had occasion to walk 

 on different parts of the banks of the Thames when the tide 

 was full, I observed objects much better on the other side 

 than when it was ebb ; and that cattle, houses, trees, &c. in 

 the meadows, as well as the mcidows themselves, that did 

 not appear at all when the tide was ebb, seemed, when it 

 was full, to be raised up very considerably. Has any of 

 your correspondents observed this with regard to the 

 Itiames, or any other river, where ihe meadows behind the 

 banks are in many parts lower than the surface of the river 

 when the tide i» full ? And if so, could they explain the 

 physical cause, or principle in optics, on which it depends ? 

 1 am, sir, yours, Sjc. 



137, St. Martin's Lane, JaMES HaLL. 



Sept. 12, 1809. 



VOLATILIZHD SILEX. 



M. Vaiiquelin has lately directed his, attention to the 

 white filamentous substance found in the cavities of the 

 Huxud matter which is attached to the sides of high fur- 

 naces ; 



