82 CARNEGIE INSTITUTION 



eminently desirable to maintain. It is manifestly impossible to give 

 a numerical rating of the seeing which shall indicate its character- 

 istics fully and without ambiguity. Nevertheless, it is convenient 

 to use a number to express one's estimate of the effect of atmos- 

 pheric conditions taken as a whole. The scale which I have used 

 in this way embraces the numbers i to 5, inclusive. 



The number 5 is used to denote seeing perfect in every way, a 

 standard of excellence that seldom obtains ; 4, excellent seeing with 

 the excellent conditions lasting for considerable intervals ; 3, good 

 seeing, but with the images less sharply defined than indicated by 4, 

 or having such conditions lasting for much shorter intervals ; 2, 

 poor seeing, images unsteady, large, or blurred, yet of such quality 

 that good work of some kinds can be done, but not that requiring 

 fine definition ; 1 , seeing so bad that good work with large instru- 

 ments is out of the question. 



At IyOwe Observatory the 9-inch telescope was erected on April 

 23, between the observatory and the reservoir, and was dismounted 

 on May 2. Observations of the sun were made during the forenoon, 

 and tests of seeing at night — till midnight or later. On one fore- 

 noon only was the day .seeing excellent. The first observations 

 were made shortly after 6 a. m. At that time the sun's limb was 

 sharply defined, and the granulations of the surface very clear and 

 distinct. Several groups of sun spots were visible, and much detail 

 could be clearly seen in both umbrae and penumbrse. At the time 

 of the earliest observation the sun's image was remarkably free from 

 passing heat waves, but this condition did not continue throughout 

 the forenoon. The seeing gradually became worse, and by noon it 

 was bad. It was the usual experience here to find the day seeing 

 grow worse as the forenoon advanced, probably owing to radiation 

 from the nearby and but scantily covered slopes of the mountain. 



The night conditions at L,owe Observatory were on the average 

 very much better than those prevailing during the day. Tests were 

 made on all clear nights. Several were found to be excellent, others 

 good, and only two bad, one of these being the night after leaving 

 Inspiration point, when a violent storm was coming on. 



In order to familiarize myself with 16-inch telescope conditions, 

 I employed that instrument on parts of five nights in looking for 

 new double stars. On each of these nights tests were made also 

 with the 9-inch telescope. The following pairs, thought to be new, 

 were found: 



