lupton: GEOLOGY OF SAN RAFAEL SWELL, UTAH 185 



After a match has been secured, the wave length of the domi- 

 nant hue is either read from the position of collimator 1 or by 

 throwing in a small hand spectroscope before the pin hole ocular 

 of 4. 



Intensities are determined by interposing between collimator 

 4 and photometer cube C, a white 180° (Whitman) rotating disk 

 illuminated by a standard lamp. This gives the intensity in 

 meter candles of each of the three component beams separately. 

 Instead of this flicker photometer arrangement, a simple equality 

 of brightness photometer may be used to determine the relative 

 brightness of any two beams. To intercompare beams 1 and 2 

 for example, the top half of the objective of collimator 1 and the 

 lower half of 2 are covered with a black card and then the width of 

 slit 1 is varied until equality of brightness is secured. This slit 

 width, compared with the original width used to secure a color 

 match, gives the relative intensities of the two beams. 



An experimental colorimeter of the type above described was 

 assembled at the Bureau of Standards in the early Spring of 1911 

 and given a thoro test. Later special optical parts were ordered 

 from Fuess and the instrument constructed in the Bureau shops. 

 This new instrument has been in constant use at the Bureau since 

 the first of January 1912 in routine tests and special research work. 

 A patent dedicated to the public has been applied for. 



Various problems arising in colorimetry are being investigated 

 with the new instrument and will be reported upon in later papers. 

 The sensibility of the instrument is, of course, that of the eye 

 (chromatic and photometric) viewing objects directly. The 

 precision attainable and the systematic errors to which the instru- 

 ment and method are subject will be reported upon later. 



GEOLOGY. — Notes on the geology of the San Rafael Swell, Utah. 

 Charles T. Lupton, Geological Survey. Communicated by 

 Alfred H. Brooks. 



The San Rafael Swell is an irregular elliptical dome, situated 

 in east-central Utah between the Wasatch Plateau and Green 

 River. It extends southwest from Price River almost to the 

 Fremont or Dirty Devil River, a distance of about 80 miles. 



