MOUNT WILSON SOLAR OBSERVATORY. 153. 



enter the slit are rendered parallel by a collimating mirror, pass through a 

 large prism, and the spectrum thus formed is brought to a focus by a second 

 mirror. A bolometer, kindly supplied by Mr. Abbot, is set at a certain wave- 

 length. As the sun's image transits across the slit, the deflections of the gal- 

 vanometer are recorded on a moving photographic plate. In this way photo- 

 graphed curves, corresponding to a number of dififerent wave-lengths, give a 

 measure of the solar radiation at points along a diameter parallel to the di- 

 rection of the diurnal motion. Several refinements of the method, which are 

 due to Professor Nichols, should lead to results of high precision. The ob- 

 servations have been completed and will be reduced as soon as possible. 



PHYSICAL LABORATORY. 



To meet the needs of experimental work, which require the use of electric 

 currents much stronger than can be economically generated on >\Iount Wil- 

 son, the construction of a new physical laboratory, on land adjoining our 

 Pasadena instrument- shop, was begun in the autumn of 1907. On January i, 

 1908, the work had progressed as far as the completion of the exterior walls 

 and roof and the excavation of the 30-foot pit in the middle of the floor. 

 During January and February the interior arrangements were for the most 

 part completed, including the cementing and drying of the pit, the laying of 

 the cement floor with conduits for electric wires embedded in the cement, the 

 construction of concrete piers for the apparatus, the installation of the elec- 

 trical machinery, and the fitting up of the chemical laboratory and dark-room. 

 About Alarch i actual investigation work began with the mounting of the 

 30-foot spectrograph in the pit and the setting up of the large electric fur- 

 nace, the construction of which had been completed in the machine shop after 

 being received from the maker. A description of the laboratory may be 

 found in Contributions from the Mount Wilson Solar Observatory, No. 27. 



The electric furnace quickly yielded results which demonstrated its super- 

 iority for spectroscopic work over any existing apparatus of the kind. The 

 work so far carried on by Dr. King has included a study of the spectra of 

 iron, chromium, titanium, and vanadium, as given by the furnace in vacuum 

 at different temperatures. The effect of temperature and different amounts of 

 vapor upon the principal lines of calcium was also observed. A series of meas- 

 urements were made with an optical pyrometer to obtain the temperatures at 

 which the various spectra were produced. Temperatures as high as 3,000° C. 

 were measured. The spectra show almost as many lines as are given by the 

 electric arc ; while the effects of different temperatures in changing the rela- 

 tive intensity of lines are of high interest when considered in connection with 

 both astronomical and physical problems. The effect of different gases in the 

 furnace, also of high pressures and the observation of absorption phenomena, 

 offer each a large field of work which has not yet been taken up. 



