A, deF. Palmer^ Jr. — Condensation in the Steam Jet. 249 



eter by which the actuating pressure of the jet could be deter- 

 mined. A globe valve in the pipe B, through which steam is 

 admitted, serves to regulate this pressure, and the stopcock S 

 allows the water condensed in the chamber to be drawn off 

 from time to time. The whole apparatus is inclosed in a 

 wooden box and the free spaces filled with hair-packing to pre- 

 vent radiation. The nozzle, situated above C and connected 

 with it by a short eighth-inch gas pipe bored smooth on the 

 inside to prevent condensation on its surface, was in the first 

 construction simply a brass block screwed to the pipe P and 

 having a hole at J about two millimeters in diameter for the 

 formation of the jet. With this arrangement it was impossible 

 at moderately high pressures to prevent spitting of the jet 

 caused by particles of moisture condensing within the nozzle 

 and being driven out by the rush of steam in such a manner as 

 to entirely mask the ordinary aspect of the jet and render accu- 

 rate measurement impossible. This difficulty was entirely 

 overcome by screwing a brass rod D to the side of the brass 

 block and heating its outer end in a Bunsen flame to such a 

 degree that the heat conducted to the nozzle was just sufiicient 

 to prevent condensation on its inside walls. Ordinarily a jet 

 formed under these conditions is quite invisible unless viewed 

 against a black background, but if it be placed in a beam of 

 direct sunlight and viewed from a point just outside that beam 

 it appears very brilliant. 



Satisfactory photographs of the jet, by reasonably short expo- 

 sures, can be made only when it is very strongly illuminated by 

 direct sunlight and the camera is placed as near as possible to 

 the line of this light without allowing it to enter the lens. 

 The arrangement of the apparatus to accomplish this end is 

 illustrated in the diagram fig. 2. The jet, J, is situated in a 

 three-sided black box having windows at AA about one inch 

 wide and three inches high. Part of a beam of sunlight from 

 a heliostat beyond H passes directly through J, while a second 

 part, after reflection at the small mirrors MM, passes through J 

 at an equal angle on the opposite side. The camera C is placed 

 midway between these two beams and at a distance from J 

 such that neither of them enters its lens. The back of the 

 camera is provided with a stop having an aperture in its center 

 one and one-half by two and one-half inches, and the plate 

 holder is arranged to slide behind this in such a manner that 

 ten images can be made on a five by eight plate. A rotating 

 shutter attached to the lens and actuated by a weight is so 

 regulated by a spring on its axis that the length of exposure 

 can be varied within sufficiently wide limits. With this 

 arrangement exposures of from one-tenth to one-half a second 

 gave very satisfactory results, and the scale of the images was 

 determined by photographing a millimeter scale so placed that 



