292 Mr. Cavallo’s ‘Description cf 
For greater conveniency, efpecially in travelling, or in fuch, 
eircumftances in which one has not the opportunity of making 
even the eafy calculations required in thofe problems, I have 
calculated the following two tables ; the firft of which fhew& 
the diftance anfwering to any angle from one minute to one 
degree, which is fubtended by an extenfion of one foot; and 
the fecond table (hews the diftance anfwering to any angle from 
one minute to one degree, which is fubtended by a man, the- 
height of which has been called an extenfion of fix feet t be- 
caufe, at a mean, fuch is the height of a man when drafted 
with hat and (hoes on. Thefe tables may be tranfcribed on a 
card, and may be had always ready with a pocket telefcope 
furnifhed with a micrometer. Their ufe is evidently to afcer- 
tain diftances without any calculation ; and they are calculated 
only to minutes, becaufe with a pocket telefcope and micro- 
meter it is not poffible to meafure an angle more, accurately 
than to a minute. 
Thus, if one wants to meafure the extenfion of a ftreet^ 
let a foot ruler be placed at the end of the ftreet ; meafure the 
angular appearance of it, which fuppofe to be 36', and in the- 
table you will have the required diftance againft 36', which is 
95 1 feet. Thus alfo a man, who appears to be 49' high, is 
at the diftance of 42 1 feet, 
T* CAVALLOi 
Wells -ftreet, 
May 26, 1791a 
