Prof. 0. Reynolds on the Flow of Gases. 185 



With delicate thermometers, such as those described, this 

 quantity is negligible (amounting to 0°*Q0Q06 C.*_) ; it is of 

 importance in the standard instrument only. The natural 

 standard No. 56117 is nearly as long as such a thermometer 

 can be made with due regard to convenience ; and the distance 

 between the freezing- and boiling-points of water on it being 

 480 millim., this error of O'Ol millim.f at each point of com- 

 parison represents O- 002 C. The value of the total scale of 

 any very delicate thermometer can thus be determined in a 

 single comparison with an error of + o, 004 C. If the ther- 

 mometer is not very much more delicate than the standard 

 itself, the error in reading it will become appreciable, and the 

 probable error in the determination of the value of the dis- 

 tance between its extreme points will be ( *004H 1° C, 



where x represents the ratio between the ranges of the standard 

 and the instrument compared with it. 



XXVIII. On the Flow of Gases. 

 By Professor Osborne Reynolds, LL.D., F.R.S4 



1. A MONGST the results of Mr. Wilde's experiments on 

 -£V- the flow of gas, one, to which attention is particularly 

 called, is that when gas is flowing from a discharging vessel 

 through an orifice into a receiving vessel, the rate at which 

 the pressure falls in the discharging vessel is independent of 

 the pressure in the receiving vessel until this becomes greater 

 than about five tenths the pressure in the discharging vessel. 

 This fact is shown in tables iv. and v. in Mr. Wilde's paper : 

 thus, the fall of pressure from 135 lbs. (9 atmospheres) in the 

 discharging vessel is 5 lbs. in 7*5 seconds for pressures in the 

 receiving vessel, ranging from one half-pound to nearly 5 or 

 6 atmospheres. 



* With the majority of the instruments mentioned in the previous 

 tables this 0-001 deg.,"or 0-01 millim., would correspond to 0°O004 C. 

 These differences include all errors due to imperfections in the cali- 

 bration-corrections applied. 



t I shall show elsewhere that the average error of reading, as deduced 

 from a large number of calorimetric determinations, is +0'011 millim. It 

 will also be shown that the error at any point due to imperfections in 

 calibration and standardization amount to +0014 millim.; but this had 

 been deduced from simultaneous observations on two different instruments, 

 and by far the greater portion of this error I believe to be due to an im- 

 perfection, hitherto uninvesti gated, which renders concordance between 

 two such instruments throughout their scales impossible, unless, perhaps, 

 the height of the column of mercury is the same in each. 



% Communicated by the Author, having been read before the Man- 

 chester Literary and Philosophical Society, NoTember 17, 1885. 



