TRANSACTIONS OF SECTION G. 819 



of paper the vibrations, north and south, east and west ; the paper, of course, being 

 driven by clockwork, and allowed to start as soon as the vibrations of the earth 

 commenced. 



Then the vertical vibrations (which have always been the most difficult to obtain 

 a record of) can be very thoroughly ascertained and recorded, by the following 

 simple arrangement. 



A light sheet-iron or steel tube, closed at the top like a small ' gasholder,' is 

 inserted in a tank of quicksilver, the centre space inside the ' gasholder ' being 

 occupied by an empty tube, so as to reduce the weight of quicksilver very materially"; 

 then on exhausting the ' gasholder ' with a ' Sprengel pump,' the tank will rise, 

 owing to the pressure of the atmosphere below it, until the column of mercury 

 balances the atmosphere ; thus the weight of the tank and mercury in it being in 

 fact supported by the atmosphere, and the ' gasholder ' being attached to the earth, 

 the ' gasholder ' may rise or fall and yet scarcely aflect the tank in any way, and a 

 rod from the tank to a multiplying lever, attached to the earth and recording appa- 

 ratus, will record the vertical vibration on a strip of paper moved by the clockwork. 



The clock will be kept always going, but the paper will be started only when 

 there is motion to be recorded. 



The attendant, on leaving the apparatus, will throw in a small catch to stop the 

 paper rollers, and the first motion of either of the levers will be made to throw 

 out the said catch, and so start the paper. The clock will be arranged to record 

 time by pricking the paper at certain intervals. 



2. The Friction of Metal Coils. By Professor H. S. Hele Shaw 

 and E. Shaw. — See Reports, p. -'i40. 



3. Steam Engine Diagrams} By M. F. Fitzgerald. 



Diagrams were exhibited showing the weight of saturated steam present through- 

 out the stroke. In a four-cylinder compound the apparent weight of steam supplied 

 was in the four cylinders — 



1st cylinder . . 1-47 lb. I .■Jrd cylinder . . 1-32 lb 



2nd „ . . 1-23 „ I 4th „ . . 124 „ 



In a Corliss engine re-evaporation took place up to about 2/3 stroke, when the 

 increase in weight of saturated steam amounted to 47 per cent, of the steam at 

 cut-off. 



In two compound pumping-engine diagrams there was in one case an in- 

 crease, in the other a decrease, in the steam apparently supplied to the second 

 cylinder. An intermediate heater is used in both of these engines. 



When the action of the cylinder sides is such as to produce a rise, followed 

 ty & fall, in the weight of steam, then at the point where there is neither evapo- 

 ration nor condensation the proportion of dry steam in mixture present is 

 given (Cotterill, ' Steam Engine Considered as "a Heat Engine,' pp. 195-6) by 



^' = Yrrr)> approximately a half; hence at this point the working substance is 



known, and theoretically the heat supply of the engine can be inferred from 

 the indicator diagram alone. 



During compression the cylinder sides nearlyalways act in this way, and are prac- 

 tically equivalent to a weight of water equal to that of the steam in clearance. 



During lead extremely rapid changes of temperature take place ; the rate of 

 transmission of heat to the cylinder surfaces rises as high possibly as 150 heat 

 units per square foot per second, confirming Professor O. Revnolds's experiments on 

 surface condensation, and is much higher than is estimated by Cotterill (' Steam 



Engine,' pp. 248-9). 



' Printed in externa in Industries, vol. v. p. 333. 



3 G 



