Dielectric influence of plate of air 251 



517] Trials of plate air i, 2, 3 and 4. [See Arts. 341 and 668.] 

 Two plates of glass nj inches square were coated with tinfoil about 11-4 

 inches diam. a slip of tinfoil extending from the coating to the other side. These 

 plates were placed upon each other with coated sides to[wards] each other and 

 kept asunder by 3 supports of sealing wax, the supports being placed a little 

 on outside of coated part and tried in the usual manner. 



Sun. Dec. 27 [1772]. Th. 50. N. 18. 

 [4 observations.] 



Mon. Dec. 28 [1772]. Th. 53. N. 17$. 



The exper. tried in same manner except that only i corner of the under 

 plate rested on machine, the rest being supported by 2 wooden pillars, the 

 places where it was supported being nearly under wax supports. 



[15 observations. Art. 668.] 



By this exper., plate air i contains i inc. el. more than D, plate air 2, -i inc. 

 el. less than D + E, and plate air 3, loj inc. less than D + E + F. 



Wed. Dec. 30 [1772]. Th. 55. N. 15. 



The supports of plate air 3 altered and called plate air 4. 



[12 observations.] 



One of the pith balls was destroyed by accident, and another put in its 

 room. 



The plate air i was made to rest intirely on machine. 



[3 observations.] 



By this exper., plate air 4 contains i inc. el. less than D + E + F, plate 

 air 2, i inch less than E + F, and plate air i, i inch more than E. It should 

 seem also that the wire Mm contained 2 inches less el. when the plate rested 

 intirely on the machine than when it rested on it only by one corner. 



The thickness of these plates of air was found by laying these plates on 

 bracket fastened to dividing machine* with or without wax supports between 

 them, and finding the division at which the new machine stood right, the knob 

 of the new machine resting on the middle of upper plate, and the under plate 

 being supported under the wax supports. By this means the thicknesses of 

 these plates of air were as follows: 



plate i = -910 



2 = -420 



3 = -288 



4 = -256 



Some experiments were made by putting bits of tinfoil between the plates 

 whether the glasses were flat, and consequently whether the measures thus 

 found were true. It seemed as if when the plates lay on each other the middle 

 of the coatings could not want more than -002 or -004 of touching, but it did 



* [Arts. 341, 459, 591.] 



