542 



SCIENCE 



[N. S. Vol. L. No. 1302 



Dr. Ernest William Goodpasture has been 

 appointed assistant professor of pathology at 

 the Harvard Medical School. 



Mr. R. S. Troup, assistant inspector-general 

 of forests, India, has been elected professor of 

 forestry at Oxford. 



At the University of Lyons, Dr. Mouriquand 

 has been appointed professor of general 

 pathology and therapeutics in place of Pro- 

 fessor Lesieur, deceased, and Dr. Policard 

 has been appointed professor of general 

 anatomy and histology in place of Professor 

 Renaut, who has retired from active service. 



the ends of the larger arc at the shore-line, but 

 there is no reason why such an accidental line 

 should determine the intersection of the two 



DISCUSSION AND CORRESPONDENCE 



AN UNUSUAL FORM OF RAINBOW 



The following is an account of a rainbow 

 which, although probably simple enough in 

 theory, was entirely new to the writer and 

 seems to be worthy of record. The refracting 

 spheres were neither falling raindrops nor 

 drops suspended in air. They were drops rest- 

 ing on the surface of a lake but kept from 

 breaking through the lake surface by a surface 

 tension effect. They probably resulted from a 

 fog which had hung over the lake during the 

 night and persisted longer than usual after 

 sunrise. The morning was unusually calm, 

 and no ripples had yet appeared on the lake. 

 The floating drops gave the surface an appear- 

 ance like that caused by a scum, but close ex- 

 amination showed the individual drops quite 

 distinctly and also showed that the light of the 

 bow undoubtedly came from them, for part of 

 the bow came quite close to the observer. 



The bow was seen about nine o'clock accord- 

 ing to the daylight-saving bill, or eight by the 

 usual local railroad time. Its appearance was 

 about as shown in the accompanying figure. 

 AB is the western shore-line of the lake, about 

 200 yards away. The bow was complete except 

 in the following particulars: the part near S 

 was hidden by the shadow of the observer and 

 that of the boat in which he sat ; and the part 

 PRQ was inverted, like a reflection of what 

 should have been the crest, the part near R 

 being somewhat less bright than the rest. The 

 ends of this inverted jKirtion seemed to meet 



, Pig. 1. 



branches. Probably they should meet at the 

 horizon. Owing to the closeness of the ob- 

 server's eye to the water-level, and the distance 

 of the shore-line, the latter would differ in 

 angular position very slightly from the true 

 horizon. Though the bow was very brilliant, 

 no trace of a second bow was visible. 



The obvious explanation of the inverted por- 

 tion is that it is formed by reflection in the 

 lake surface, either directly before or directly 

 after the light passes through the drop. If the 

 light enters the top of the drop and is after- 

 ward reflected from the lake-surface, the re- 

 flected ray vwU clear the drop if the elevation 

 of the sun is greater than 21°. 6. If it is first 

 reflected from the lake and then enters the drop 

 at the angle of incidence proper to give rise to 

 minimum deviation, the sun's elevation must 

 be less than 20°. 4 in order for the incident ray 

 to clear the drop. These figures are calculated 

 on the assumptions that the drop is spherical, 

 that it rests on the surface, and that the angle 

 of the bow is that given by the elementary rain- 

 bow theory. 



H. M. Reese 



TJniversitt op Missouri 



a simple device for illustrating 



OSMOSIS 



The difficulty of preparing a " leak-proof " 

 aijparatus to demonstrate osmosis by the use 

 of parchment and thistle tube, led me, last 



