MOUNT WILSON OBSERVATORY. 285 



For stars of intermediate galactic latitudes similar results are obtained 

 in a somewhat different way. 



It appears that for the greater part of the system the linear velocity 

 is practically constant and equal to about 19.5 km. per sec. The 

 direction of the rotation is indeterminate. If we assume that part of 

 the system moves one way and the rest in the opposite direction, the 

 relative velocity of the two groups, for the bulk of the stars, is 39 km. 

 per second. 



We are thus led, in a perfectly natural way, to a complete theory 

 of the phenomenon of star-streaming, which agrees qualitatively and 

 quantitatively with what we know about these streams. That the 

 theoretical stream-lines are curved, whereas Professor Kapteyn has 

 thus far supposed them to be rectilinear, offers no difficulty, if it turn 

 out, as in all probability it will, that the sun is not very near the center 

 of the system. For in this case the curvature of the stream-lines, 

 within the domain of the stars which have served for the derivation of 

 the star-streams, must be inappreciable. 



Further consequences of the theory as well as a number of defects of 

 this very provisional solution are outlined in a forthcoming Contribu- 

 tion. 



PHYSICAL LABORATORY. 

 INSTRUMENTS. 



The solenoid nrngnet for high fields, described last year as under 

 construction, was assembled during the winter and tested. The 

 cooling system proved to be adequate, the magnet carrying its full 

 load of 4,000 amperes. Rough measurements indicated a field-strength 

 of 33,000 gausses in the tubular space of 5 cm. diameter within the 

 solenoid. After experiments, described later on, had been made with 

 a vacuum furnace and then with a Stark-effect tube in the solenoid, 

 the latter was dismantled, rewound, and considerable time spent in 

 improving the kerosene-circulation system to guard against the accu- 

 mulation of water, which tended to produce electrolysis, and sedi- 

 ment, which obstructed the flow. These changes having been made, 

 the apparatus is again ready for service. 



In order to study the effect of a magnetic field at different angles 

 to the lines of force with reference to sun-spot phenomena, a second 

 solenoid was constructed of copper tubing, water-cooled, the coil 

 having an internal cavity of sufficient size to permit the rotation 

 of a small furnace up to an angle of 60° to the lines of force. This 

 solenoid, excited with 1,200 amperes, gives a field of about 8,000 

 gausses, and is especially adapted for the observation of absorption 

 spectra. 



The furnace with water-cooled contacts, constructed last year, hav- 

 ing proved very effective for high-temperature w^ork, a chamber was 

 constructed so that it may be used as a vacuum furnace. This con- 



