﻿24 Mr. Carl Barus on 



long as the inflowing air exceeds a certain minimum quantity 

 and the nozzle is of average smoothness. A full discussion of 

 all these points will be in order when I come to measure the 

 thermal distribution within the colour-tube, and particularly 

 in the neighbourhood of the nozzle of the jet. 1 will then 

 show to what extent each jet possesses special hydraulic pro- 

 perties *. In a general way the jet may be advantageously 

 compared with a Bunsen flame. For just as in the one case 

 the blue cone is a locus indicating the speed of chemical 

 action |, under the given conditions of mixture and efflux, so 

 in the steam-jet the transparent cone of vapour indicates the 

 rate at which condensation takes place. Given the rate of 

 efflux of steam, a photographic method may then be easily 

 devised for expressing the speed of condensation % numerically. 



The fact that pin-hole jets are quite sufficient makes the 

 practical construction of the apparatus (Plate V. fig. 1) 

 on a small scale an easy possibility. A globular copper 

 boiler, 5 inches in diameter, and a sensitive steam-gauge with 

 a capacity of less than 15 pounds, are available for generating 

 the steam and recording pressure. 



6. Results. Normal Atmosphere. — The results in hand are 

 necessarily in very great number, for the case is one in which 

 the observer has to construct the mean value or path, when 

 the observations themselves are unavoidably discrepant. It 

 will therefore be expedient to avoid cumbersome tables, by 

 expressing all the data graphically. An ulterior advantage 

 is gained in this way, inasmuch as the broad features of the 

 phenomena are at once evident to the eye. 



In the chart, Plate V. fig. 2 (and in all succeeding 

 charts), the abscissas indicate the temperature, in degrees C, 

 of the air entering the colour-tube at C (fig. 1) ; or, in other 

 words, the registry of the thermometer t. The ordinates 

 show the pressures in centims. of mercury under which 

 the steam is forced out of the jet. The points of the 

 curve between and about 40 cm. then show the corre- 

 sponding values of air-temperature and steam-pressure, at 

 which the blue- violet (first order) field seen in the colour-tube 

 merges into opaque. The points of the curve lying quite 

 above 40 cm. show the conditions at which the brown- 

 yellows of the first order just emerge from the opaque. 

 Curves indicating the approximate loci are drawn through 

 the points. 



* Agreeing with the results of Aitken, I. c. 

 f Cf. W. Michelson, Wied. Ann. xxxvii. p. 1 (1889). 

 X A discussion of this method of investigation is given in the 

 Bulletin. 



