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216 in concrete form a vast amount of valuable information. 2 With the charts he has worked out the dip of any line of given length is shown, the approximate pull being known, or vice versa. The ordinary thrust of any steamer under normal conditions is easily calculated and with the exercise of a little discre- tion the master has always at hand a ready check on the length of line best suited to existing conditions. It is needless to point out that a dip great enough to foul bottom on the Grand Banks in 70 fathoms is ac- complishing nothing except adding enormously to towing resistance. Closing Discussion. T. S. Kemble: Mr. Riley states that the resistance of towing machines to paying out line is not due primarily to the admission of more steam but rath- er to the compression of steam already in the cylinders, I have made some study of this sub- ject and believe that we may accept his explanation as applying to that type of machine which is equipped with a slow opening automatic valve, but the 'indicator cards' on Plate 1 and Plate 2 show clearly that it does not apply to machines with a quick opening valve, although the machine from which those cards were taken has not so swift a valve opening as is now used on this class of machines. In one set of cards, taken with a heavy head sea, I found THE MARINE REVIEW mission pipe, but this was the only case in a long series of rolls taken on various occasions under all sorts of weather conditions. The general opera- tion is shown by the indicator cards to be due to admission pipe pressure. Mr. Riley's theory of operation im- plies the assumption that the machine has stopped winding in just before one crank reached dead center. We would have one cylinder full of steam and the other cylinder half full, and if for the sake of concrete illustration we assume a volume in the clearances and passages back to the automatic valve equal to another half cylinder volume, we would have two full cylinder vol- umes of steam. It will also simplify the illustration if we consider the steam as a perfect gas in which the product of pressure and volume is constant and neglect all consideration of initial con- densation, wire drawing, etc., which are aside from the point under discussion. The overhauling of the engine for nearly half a stroke would force all the steam into the clearances and pass- ages and the half of one cylinder, cut- ting the steamy space in half: and doubling the pressure which was pres- ent at the beginning of the operation. The steam then re-expands to the original pressure and repeats the cycle. If, however, the machine should stop just after one crank had passed the center instead of just before, there would be present at the beginning only one full cylinder volume. As soon as J uly, 1909 the steam space would be doubled and the steam pressure cut to half that present when holding the load. The next half stroke would compress this steam to the original pressure and re- expand it to one-half again. The action when the machine began paying out from any position other than those described wouid be a com- promise between the two. I have prepared diagrams _ illustrat- ing this action. The steam pressure holding the load is taken at 65 Mb, absolute, the back pressure at 25 Ib. absolute and the pipe line pressure at 130 Ib. absolute. Fig. 1 is a conven- tional card illustrating the changes in pressure when the machine is over- hauled from the position first described, in which we have two full cylinder volumes at the beginning. Fig. 2 is a similar card illustrating the changes in pressure when there is only one full cylinder volume at the beginning, Fig. 3 is a similar card illustrating the changes in pressure when there are two cylinder volumes of steam present at the beginning, and when the valve opens very rapidly, giving a very large area through which the steam may enter. In some machines the automatic valve is now opened to give an area equal to the steam pipe area in two strokes of the piston, and as the first motion of the machine is relatively slow, the pressure in the cylinders is almost if not quite as high immedi- a pressure in the cylinder a trifle the machine began to be overhauled ately after the first half stroke as it is higher than that reported in the ad- this crank would re-cross the center, with the valve wide open. oS Tas ZS als FAs Plate 5 a tere KPA 20g me es SS os "| L | lA va ae LY | LA 1 Y| VA 4] YY iY Atm. Fig. 1 A ry aeT AUN oh, a *K eon ta ae? 3 a s4- "Ye Sh me g : I 3 : | Ca ae eer | | ee Lal ea 3 Atm. ead wl | eg E = Fi q. 2 an 4, obs +s rt p>- --Y-- te Sy AVE Ms ic \ ae te Nee Le ae RTA a ve PI ae TT TAT LTS | lm al nN / MV \ | AO oe iY] Atm Fig 3