214 On the Lubrication of Resistance-Box Plugs. 



accurate work this, however, is of no consequence as the 

 plug-resistance must in any case be measured ; but when 

 this has been done, it is highly desirable that the resistance 

 should remain invariable, and this end is, it appears, best 

 attained by the use of vaseline. We now give in Table B 

 summaries of the results obtained with three other second- 

 class boxes. 



Box No. II. 

 having 

 17 plugs. 



Table B. 



Before 

 lubricating. 



f Number of determinations = 10. 

 Maximum total resistance = "00728 ohm. 

 Minimum „ „ = -00452 „ 



Mean „ „ = -00593 „ 



Variation = ±"00138 „ 

 Percentage „ = ± 23 



After lubricatiug 

 with vaseline. 



10. 



•00496 ohm. 

 •00434 „ 

 •00458 „ 



±•00031 „ 



+6-1 



( Number of determinations= 7. 7. 



"R Ya ttt i Maximum total resistance^ 0"2357 ohm. 0'0364 ohm. 



havmi J Minimum „ „ = "0385 „ "0336 „ 



having -j Mean ^ ^ = . 099Q ^ . 0343 ^ 



Variation = ± -0654 „ +-0008 „ 



^ Percentage „ ±66 +2-3 



4 dials. 



Box No. IV. 



having 



17 plugs. 



Number of determinations = 10. 



Maximum total resistance 

 Minimum ,, ,, 



Mean ,, ,, 



Variation 



^ Percentage 



•01597 ohm 

 •01302 ., 

 •01397 „ 

 ±•00079 „ 



= ±57 



10. 



•01241 ohm. 

 •01148 „ 

 •01188 „ 



±•00031 ;, 



+2-6 



We observe that for each of the above-named boxes a very 

 marked improvement was secured by the application of 

 vaseline ; and in the case of the dial-box (No. III.) the 

 gain was very great. In general, we find that on bringing 

 newly lubricated plugs or switches into use, their joint re- 

 sistance diminishes for a short period, and then becomes for 

 all practical purposes constant. 



An oil-bath has this advantage over vaseline in that the 

 plugs are automatically and fully lubricated with every 

 setting • but, on the whole, vaseline is much more convenient 

 in use, and in so far as we have been able to discover, the 

 residual variations in plug-resistance are decidedly smaller 

 than when a liquid lubricant is employed. 



As confirmatory evidence of the beneficial effects attending 

 the application of vaseline, we give in Table C a summary of 

 the results obtained by experimenting with a first-class 

 resistance-box fitted with 17 Drugs. 



