On the Rate of Increase of Und rgroun ■ T np ratures, 457 



The necess t\ of idopting so i m • ms to j \ i nt tin < in ula- 

 tion of water in bores, has for some time been forcing itself 

 upon the attention of your committee. Many of the observa- 

 tions taken by their observers have contained such pidpable 

 evidence of convection as to render them manifestly useless for 

 the purpose intended ; and in the light of the Sperenberg 

 experiment it is difficult to place much reliance on any obser- 

 vations taken in deep bores without plugging. The selection 

 of a suitable form of plug is now occupying the careful atten- 



Herr Bunker's paper gives a very full account of the different 

 kinds of plug employed at Sperenberg. 



For stopping the mouth of the advance-bore the plug had a 

 was of hard wood, strengthened by two iron 

 iii)_-. 01 i at e k b cud. and covered with a layer of tow five lines 

 thick, outside of which was thick and strong linen, nailed above 

 and below to the wood, through a leather strap. It was lowered 

 into its place by means of the iron rods used for boring; and, 

 when in position, was pressed home by a portion of the weight 

 of the rods. The plug curried th ■ th -nnometer suspended from 

 it. Its exf. iced by means of a screw on the 



beam of the boring machine, iti order to avoid a sudden jerk, 

 which might have broken the thermometer. The force which 



was 1 I >essar\ tor tl is Parting the plug, as well as the 



impression observed upon it when withdrawn, showed that it 

 ■■_ht. To insure a good fit. the top of the advance- 

 bore had been brought to a sail 



removed, bv m ans of revoh i i.u ' itting-tooL Herr Danker 

 - '■ 

 but r mt ii onlin u >. 1 n 1 r. ck it would be better to make the 

 bottom of the main bore flat, and to close the advance-bore by 

 an elastic di*c pr<^ed over it. The method of observation by 



bore, a time when it - dim mlt t » a\ .id . i »r ismg from the 

 heat generated in boring. The expense of making an advance- 

 bore at each depth at which an observation is required is also 



^AnifherkSdoMug devised bv Herr Danker, and largely 



used m 1m f ,< n-i^ d »t a bair of vrv <t.>ut ha- 



:■■ ,>~ \ ■••:■ ■ 

 , ..:.■ -....- ■_ - ■ • ■ ■■ - 



.oi tic bore On the-u-^tioiiotbore- 



_-.a, ve,-. like the 

 h u ,p distorted into an oval by pressing against its 



