THE PLOW OF WATER IN WOOD-STAVE PIPE. 21 



OPEEATION OP GAUGES. 



From observations on the ground or study of the profile, the 

 pressure in the pipe was known roughly. In assembling the gauge 

 the proper number of iron-pipe units was installed in the long leg 

 of the U so that the two ends of the mercury column balancing the 

 pressure in the pipe would appear near the mid-point of the glass 

 gauge tubes. 



The gauge, as assembled in figure 3, was set up beside the tapped 

 pipe, the glass tubes being made truly vertical by means of a plumb 

 bob. Shade was always provided for the gauges. 



With the cocks I and L open and G closed, mercury was filtered 

 into the tube T. A paper-lined glass funnel was inserted at the top 

 of T. The mercury filtering through a pin hole at the bottom of 

 the paper funnel was thus cleansed at each experiment and the 

 meniscus in each tube was made bright and clear. Mercury filtered 

 into a tube of smaU diameter in this manner wiU fill up without air 

 bubbles, but if it is poured into such a tube air bubbles will occupy 

 long reaches of pipe and may not be found if they occur in the iron- 

 pipe sections. When both legs of the gauge were fiUed to near the 

 top of the lower glass, I was closed and G opened until the mercury 

 column in M was pressed well down in the gauge, when G was again 

 closed. Mercury was then added and G was opened from time to 

 time untn it might be allowed to remain open, the pressure holding 

 the mercury column in sight on both glass gage legs. 



At this time there was probably a mixture of air and water above 

 the mercury in M, but the air was driven out by alternately closing 

 G and opening I for an instant. In using the gauges L was closed 

 and G and I opened every few minutes, so that water and any accu- 

 mulated air bubles might be blown out of the pressure tube between 

 the gauge and the wood pipe. 



Because of the use of unequal legs on the gauge there was danger 

 of blowing mercury out of the gauge at I unless the cocks L and G 

 were operated most carefully. To catch the mercury in the event 

 of such an accident, the tube J was discharged into the bottle K 

 which included a glass tube open to the air so that water was freely 

 discharged but the mercury caught. 



Pulsations were nearly always present and as simultaneous readings 

 of both low and high gauges were necessary in order to determine 

 the length of the mercury column, readings were made in the follow- 

 ing manner: 



Pulsation effect was reduced by partially closing either L or G 

 imtil the mercury was barely "alive." This assured an average 

 length of colmnn. The cock was then completely closed, leaving a 

 "dead" mercury colmnn of the proper length. Both low and high 

 gauges were carefully read to thousandths after which the cock was 



