406 



KEPOET 1892. 



tliey make, never use any other means of obtaining records but a small 

 pen supplied with aniline ink, which invariably continues to act for at 

 least tweuty.four hours, and will, under favourable conditions, continue at 

 work for weeks or even months. Of course, the composition of the ink 

 used has been the subject of very careful study by that firm, and great 



Fig. 32. 



care must be taken to prevent pressure with more than the very slightest 

 force against the surface of the paper, or it scrapes up a sort of fur, which 

 soon stops the action of the pen. 



The spiral has been used with various instruments where it is more 

 convenient to turn the marking arrangement about its axis than to move 

 it to and fro ; thus, in the self-recording water-meter devised by the 

 writer ' this arrangement was used, also in the instrument for giving the 

 direction of the wind manufactured by Messrs. Bailey & Co. for the 

 Salford Town Hall. It is clear that the spiral, being in contact with the 

 paper wound round a cylindrical drum, will mark it at any point along 

 the drum corresponding to the angle through which it has been turned. 

 Fig. 34 shows the recording portion of this instrument. 



The last two means of recording to be mentioned, viz., g and h, are 

 the only two which are suitable for obtaining a diagram where it is im- 

 pex-ative to have no friction at all at the recording-point. 



' ' The Measurement of Velocity,' by H. S. Hele-Shaw. 

 vol. Ixix. p. 361. 



Min. Proc. Inst. C.E., 



