262 CARNEGIE INSTITUTION OF WASHINGTON. 



for this work, the pressure ranging from a few millimeters of mercury 

 up to one atmosphere. The method of simultaneous exposures, which 

 has proved so useful in our previous experience with both gratings and 

 interferometers, will be followed in this exacting work. 



SPARK SPECTRA. 



For his work on the spectra of electrically exploded wires, Mr. Ander- 

 son has built a condenser of about 1 microfarad capacity, which can be 

 operated at 25,000 volts. Brilliant sparks of extremely violent charac- 

 ter are produced by the discharge of this condenser, especially when the 

 inductance in the circuit is kept very low. On account of its great 

 capacity, the condenser is charged from the secondary of a 5-k. w. high- 

 voltage transformer through a mechanical rectifier. Messrs. Anderson 

 and Babcock have together used this apparatus with the 15-foot con- 

 cave-grating spectrograph to secure photographs of the spark spectra 

 for iron, titanium, chromium, nickel, and vanadium over the region 

 X3000-X7200. The plates have been studied by Miss Keener, who has 

 classified the lines as to general character, including sharpness, symme- 

 try, etc. Since this source of light presents the most extreme type of 

 spark spectrum thus far obtained in om* laboratory, the photographs 

 form a valuable reference map for comparison with other sources. 



SPECTRA OF EXPLODING WIRES. 



During the year Mr. Anderson has been engaged principally in the 

 study of the spectra of electrically exploded wires. The investigation 

 is a first attempt to imitate as far as possible in the laboratory the con- 

 ditions which must exist when a meteoric particle moving with very 

 high velocity encounters a resisting medium such as the atmosphere 

 of the sun or a star. The large amount of kinetic energy possessed by 

 the particle is transformed into heat, undoubtedly in a very short time. 

 This results in a very rapid vaporization of the materials constituting 

 the particle itself. In order to produce a very rapid vaporization of a 

 substance in laboratory experiments, the discharge of a large con- 

 denser, charged to as high a voltage as possible, was employed. The 

 substance to be vaporized — metals in the present case — was inserted 

 in the condenser circuit in the form of a fine wire. When the dis- 

 charge takes place the vaporization is so rapid that it can be de- 

 scribed only by the word explosion. If the gases formed in such an 

 explosion are confined slightly, the spectrum is continuous with the 

 lines of the substance composing the wire appearing in absorption. 

 The spectrum of iron produced in this way was studied from X2200 to 

 about X6600. All the lines except the pronounced enhanced ones are 

 present. The intrinsic brightness of the explosion was found to be 

 of the order of 100 times that of the solar surface, corresponding to 

 a black-body temperature of 20,000° C. 



