Conversion of Cameos into Intaglios, 6?c. 101 



morning not being very clear, but in a pretty light cham- 

 ber, I viewed a watch hanging against a plain wall, through 

 the optical tube ; the whole of it appeared concave, and 

 fixed into the wall. I also observed some flies that were 

 running about the wall, and they appeared in like man- 

 ner. I also viewed a small globe of a thermometer filled with 

 red spirit, and this also seemed hollow, and fixed within the 

 frame. I found the same to happen with the round parts of 

 garments of all colours, and with the brazen protuberances 

 of a small cabinet ; all which appeared concave, and deeply 

 sunk into the cloth and wood. I also viewed a small stag's 

 head, cut in wood, and hanging horizontally on the wall ; this 

 also appeared concave, and fixed into the wall. 



After this, I observed a ball of one of Fahrenheit's ther- 

 mometers, full of quicksilver : but it did not change its natural 

 convexity ; nor did the empty glass ball of the inverted ther- 

 mometer hanging against the wall, though the lower ball of 

 the same, filled with red spirit, and that also of Fahrenheit's, 

 filled with spirit, lost their convexity. Hence, I presently con- 

 cluded, that white or shining uncoloured bodies, appear under 

 the focus of this tube in the same manner as they appear to 

 the naked eye ; at the same time, I must fairly acknozvledge, 

 that an assisting friend has sometimes made observations di- 

 rectly opposite to mine in the same circumstances ; nay, in a 

 darker day, I myself have fund my observations quite contrary 

 to those I had made the day before. Hence, though the obser- 

 vations with the seal held constantly the same, I imagined 

 there must be some particular circumstances hitherto undis- 

 covered, in which these objects appeared thus perverted. T 

 therefore endeavoured to discover some certain laws, accord- 

 ing to which these perverted objects appeared when exposed 

 to these foci, and some others according to which they con- 

 stantly appeared as when they were exposed to the naked eye. 

 After various experiments, I partly obtained my end. 



As often as I viewed any object, rising upon a plane, of 

 what colour soever, provided it was neither white nor shining, 

 witli the eye and optical tube directly opposite to it, the ele- 

 vated parts appeared depressed, and the depressed parts ele- 

 vated, as it happened in the seal, as often as I held the tube 



