418 



Mr. J. H. Reeves on an Addition 



(1) The accuracy of the ratio - ; 



if 



(2) The accuracy of the value of r ; 



(3) The sensibility of the galvanometer. 



As far as condition (1) is concerned, x and y being taken 

 from a good box have an error of certainly less than O'l 

 per cent. 



Condition (2) is discussed later, and the effect of condition 

 (3) can be best seen by reference to tests made in the labora- 

 tory of the Central Technical College with the apparatus 

 arranged as in fig. 3, except that, at the start, the battery 

 consisted of a single Daniell cell, the galvanometer being a 

 four-coil reflecting one having a resistance of 687 ohms and 

 a sensibility of about 400 scale-divisions per microampere. 



Table I. 

 Tests made on high conductivity copper, R= 



100,000 



ohms. 



No. of 



wire. 



S.W.G. 



Diameter, 

 mils. 



X. 



Observation. 



R. 



Specific 

 Gravity. 



Specific 

 Resistance. 



Conductivity. 



Matthiessen's 



Standard. 





f 



4324 



^ div. deflexion left. 



1 











22 



28-07 \ 

 [ 



4326 



4328 

 2618 



Small „ right. 

 1^ div. „ right. 

 1 „ „ left. 



I 0-04325 

 1 



8-841 



1-616 





100-3 



20 



355 j 



2620 



2622 



Small „ left. 

 ^ div. ,, right. 



1 0-02621 



8-918 



1-572 





1031 



18 



48-8 [ 

 ( 



1421 

 1422 



802 



i „ „ left, 

 i „ „ right. 

 3 „ „ left. 



1 0-014215 

 1 0-008032 



8-912 



1-602 





1011 



16 



64-2 \ 



803 



i „ „ left. 



8-907 



1-572 





1031 





\ 



804 



2 „ „ right. 



J 













80-1 J 



515 



2| „ „ left. 



| 











14 



516 



Small „ left. 



10-005163 



8-888 



1-566 





103-4 





517 



1 div. ,, right. 



J 











12 



103-2 [ 



314 

 315 



1 , „ left. 

 1 „ „ right. 



j 0003145 



8-904 



1-585 





102-2 



— 



106-9 [ 



291 

 292 



1 „ „ left. 

 5 „ „ right. 



j 0-002916 



8-940 



1-580 





102-6 



— 



103-8 | 



308 

 309 



H „ „ left. 

 1 „ „ right. 



1 0-003086 



8-870 



1-588 





102-4 



— 



104*2 { 



309 

 310 



2 „ „ left. 

 | „ „ right. 



] 0-003098 



8-891 



1-580 





102-6 





Matthiessen's standard has been taken to be a specific resistai 



ice (resistance 







per cubic centimetre at 0° O.) of 1-620 International Microhms. 









Towards the end of this table it will be seen 1 



;hat even a 







sensitive galvanometer barely allowed an accur 



acy of 0*1 

 red, and a 







per cent. The Daniell cell was therefore remo^ 







small a 



ccumr 



dator with a resistan 



ce of 2 o 



bms in 



series wi1 



h 





