TRANSACTIONS OT THE SECTIONS. 241 



parts, viz. : — (1) a steam-nozzle of annular cross section, discharging steam in the 

 form of a hollow cylindrical body of a thickness of wall of not more than -02 (one 

 fiftieth) of an inch; (2) a mixing-chamber, with contracted annular inlets for the 

 air, equal in area to its least sectional area, and of a length equal to from five to six 

 diameters ; (3) a parabolic delivery -pipe of considerable length, in which the 

 mixed current is gradually brought to the condition of comparative rest, and its 

 momentum or living force is reconverted into potential force or pressm'e. 



The result of a long series of experiments leads to the conclusions : — (1) That 

 the quantitative effect of a steam-blower depends upon the amoimt of contact sur- 

 face between the air and steam, irrespective of the steam pressure, up to a certain 

 limit of compression, where the impelling action ceases ; (2) that the maximum 

 attainable differences of pressm-e increase, under otherwise similar circumstances, 

 in direct proportion with the steam pressure employed ; (3) that the quantitative 

 effect produced is regulated (within the limits of efficient action of tlie instrument) 

 by the weight of air impelled, and that therefore a better djTiamical result is 

 realized in exhausting than in compressing air ; (4) that the limits of difference of 

 pressure attainable are the same in exhausting and in compressing. 



It was stated that with this apparatus a vacuum of 24 inches of mercuiy had been 

 obtained, and that with two of these apparatus a working vacuum of 10 inches of 

 mercuiy had been maintained at one end of a pneumatic despatch-tube 3 inches in 

 diameter, through which carriers were propelled at the mean rate of about 1000 feet 

 per minute. 



Auiomatic Gauge for the Discharcje of Water over Waste Weirs. 

 Bij Thomas Stevenson, F.R.S.E., M.I.C.E., C.E. 

 The author stated that, in order to ascertain the amoimt of available rainfall, 

 which is so important in questions of water supply, it is necessary to gauge the 

 quantity of water which escapes at the waste weirs of reservoirs. Observations 

 made only once or twice a day cannot supply the infoiiuation. It is proposed 

 to placea tube perforated vertically with small holes, the lowest of whicli is on a 

 level with the top of the waste weir, so that, whenever water passes over the 

 weir, it also passes through the holes in the tube. The water is collected in a 

 tank capable of holding the discharge for a certain number of hours ; the quantity 

 so collected is a known submultiple of what passes over the weir. The discharge 

 through the holes is ascertained by experiment. This self-acting apparatus will 

 render the continuous observations of floods unnecessary. 



TTiermometer of Translation for recording the Daily Changes of Temperature. 

 Bg Tjiomas Stevenson, FJi.S.E., M.I.C.E., C.E. 



The author described what he termed a thermometer of translation, which con- 

 sisted of an expansible body with a needle-point at its upper end, and which, when 

 expanded by the sun, is fixed at its upper end by a needle-point catching into fine 

 teeth cut in a sheet of glass or other material of small expansibility placed below. 

 "When the sun is obsciu'ed, the upper end being fixed, the conti-action raises the 

 centre of gi-avity of the bar. In this way the daily march or creep of the bar 

 chronicles the change or changes of temperature. Mr. Stevenson also described 

 two different methods, suggested by his friends Professors Tait and Swan, for 

 increasing the amount of expansion of the material employed. 



On improved Ships of War. By Michaei Sc ott. 



On a Uoad Steamer. By W. Thomson. 



The great feature in the construction of this machine is the use of a rciy thick 

 india-rubber tire, to the outer circumference of which is attached a chain of flat 

 plates of iron. These india-rubber tires not only completely prevented hard shocks 



1871. 16 



