EXPERIMENTS WITH IONIZED AIR. 3 



that the tubes slide into tlie smigly fitting envelope /•, and the system may tliere- 

 fore be shortened for observing very intense coloi's, or lengthened ior faint colors. 

 Either end of A^l may be n)tated. 



Coloi- tests are as a rule more satisfactory for (quantitative work if some fidu- 

 cial field is at haud for comparison. Figure 2 therefore consists of two color tubes, 

 identical in every respect and admitting of an independent use of both eyes. Sky 

 light is introduced by the minors M and M'. The observer looks down into both 

 windows,^ and g', at once. The two tubes may be connected rigidly by the doulile 

 bridge, and supported from a stout rod, «. If the jets are identical and communi- 

 cate with the same steam box, the colors seen by both eyes should be identical. 

 This state of things is found by trial. Supposing, therefore, the right tube is left 

 without intei'ference, the other tube may be manipulated in various ways. In all 

 such cases the two tubes are connected in multii)le, as it were. But if the jet be 

 i-emoved from A' A', and the discharge from A A, after passing through a suitable 

 length of wide tube, be eventually passed through A' A', without furthej- interfer- 

 ence, the two tubes are in series. This adjustment is shown in figure 4 and leads 

 to interesting application of the apparatus. 



On reviewing the earlier experience it appears that the adjustment of air and 

 steam which secures the clearest field must be made as nicely as the adjustment of 

 air and gas in a Buusen burner. Otherwise the colors ai-e either dull or faint, quite 

 apart from tempei'ature or pressure conditions. Often the efflux may be stimulated 

 to advantage by an auxiliary ventillating tube at B, containing its own jet, without 

 interfering with the color tube itself. Whenever possible it is preferable to take 

 the air entering 6' from a room heated ueai-ly equally throughout. In cases where 

 this is not possible, the train repi'esented in figure 3 is useful. Here a, g, are the 

 windows of the color tube AA^ j the jet, and M the mirror. B is the efflux tube 

 for mixed steam and air, C the influx tube, showing the thermometer, t, in place. 

 The air entering O is taken from the outside atmosphere, the three influx tubes, 

 E, D, F, passing through the window frame, W. Valves are iusei'ted in each of 

 these tubes, as at e, y, 7^, so that the quantity of air passing through each of them 

 may be regulated or quite shut off. In winter when the valves are open, the air 

 rushes through the tubes with considerable velocity, even when the jet j is not in 

 action. This velocity increases with the steam j)ressure actuating the jet. Under 

 no circumstances must the valves be so far closed that there is not free influx of air 

 at G. The tube ^is clear, and the air passing through it has the temperature of 

 the atmosphei'e. The tube D discharges into ^and is provided with a drum con- 

 taining a coil of thin lead pipe. About 20 turns of pijJe, each about 5 cm. in 

 diameter, and a di'um about 35 cm. long and 10 cm. in diameter, are more than 

 sufficient. In winter time steam is passed through the lead pipe; hence by suita- 

 bly regulating the valves h and /, the air flowing through C may be kept at any 

 desirable temperature, since temperatui'es between 9° and 40°, only, are needed 

 for the present purposes. In summer time, chilled brine or an expanding gas would 

 be similarly serviceable. 



The auxiliary tube,, also ^discharges into E, and is useful for increasing the 



