42 PROFESSOR C. V. BOYS ON THE 
Measures of Wires with Optical Compass. 















| | 
Side. | Wire. Scale. | Head. | Correction. 
| | 
Atppanentorich ties Rach tess oy eae 6:03 641 
- guy! | ett ceaaewical ae 04 (+4) 029 
| | + 000025 
eS left Right (605+2). .)| 603 | 955 
90 ff somo Pulte eg lg 6 20 04 (+4) 357 
| 
Thickness. 
Apparent left side. | Apparent right side. 7 
| Left. Right. 
6:03955 | 603641 "02357 02955 
05357 | 05029 “00029 00641 
598598 | 598612 02828) \)./)) 02374 
5'98612 
Mean . . 5°98605 centre to centre. | 
+ :000025 correction. | 
5°986075 corrected value. | 


The (+ 4) after ‘04 indicates that when the right microscope was exactly on the 
division 6°03, the left one was, by eye estimation, at 044, or yo of a division above 
04. Since also the screw-head reading has passed 1000, or a complete turn, and has 
risen in the two cases to 029 and 357, °05 is the quantity that must be written in 
the subtraction below to find the distances from side to side of the wires. 
(6:05 + 2) means that 6°05 was the division seen when the scale was put in its 
former place and that two whole turns of the screw were needed to bring 6°03 into 
view again. It was because there was only one division at the supposed zero ‘04, 
that the scale had to be pushed forward so as to bring 6:03 into view again, and 
‘04 and 6:03 were used to measure the apparent left (but really right) sides of the 
wires. 
Section d.—Place the two microscopes in the centre pair of grooves and bring 
them both in succession to focus on the same wire, adjust the focussing collars, if 
necessary, so that when pushed up to their collars they are each in exact focus. 
Having the proper back window, figs. 13, 14, in position, withdraw the microscope 
and move the traversing slides till the microscope will be able to slide forward and 
view the fibres. Push both up to their collars and move laterally until the 
fibres are found. If, as is probable, they ave out of focus, ascertain by moving either 
microscope by hand in its grooves whether the error of focus is in the same direction 
for both. If it is not, slowly turn the lid, using a lever bearing upon the pin of the 
first wheel of the train and entering the nearest tooth on the edge of the lid. This 
