September 10, 1920] 



SCIENCE 



249 



with the spark has the same effect as increas- 

 ing the current. It is possible to obtain the 

 glow from hot calcium oxide providing the 

 discharge is kept very small. 



The shape and position of the electrodes have 

 no appreciable influence on the production of 

 this glow. It is produced equally well from 

 platinum and from iron electrodes and in 

 tubes made from soda and from lead glass. 

 It does not appear to depend on the purity of 

 the mercury. 



It requires approximately .001 sec. for the 

 glow to die out after the exciting current has 

 ceased. As a result of this continuance of the 

 glow the radiators may continue to give light 

 while being carried with the current of mercury 

 vapor for 20 or 30 cm. 



These radiators do not appear to be charged. 

 Thus if the luminous vapor containing them is 

 passed through wire gauze, no effect is pro- 

 duced on the intensity of the continuous spec- 

 trum when the gauze is charged negatively. 

 This is quite different from the behavior of 

 the radiators of the line spectrum which may 

 be entirely removed by this means. It is pos- 

 sible in this way to obtain the continuous 

 spectrum without any of the line spectrum 

 appearing. 



As far as has been observed there are no 

 lines or separate bands in the spectrum here 

 described. It is, however, possible that a 

 spectroscope better than the one at the com- 

 mand of the writer may show such lines. 



It appears probable that we are here dealing 

 with a vapor which is intermediate between a 

 gas and a liquid. When a gas is condensing 

 there must be a time when two or more atoms 

 have conibined to form clusters. Such a vapor 

 might be expected to give a spectrum inter- 

 mediate between a line spectrum as given by 

 a gas and a continuous spectrum as given by 

 a liquid or solid. This is a fact the kind of 

 spectrum here observed. 



Further work is being done on the subject 

 and it is expected that the results will soon be 

 published in more complete form. 



C. D. Child 



Colgate TJniversitt, 

 August 6, 1920 



A NEW VARIETY OF THE ROOF EAT 



During the second week of March of this 

 year Miss Jane F. Hill, one of our students, 

 brought to the laboratory about a dozen rats, 

 which had been taken on her father's farm. 

 The farm is located fifteen miles from Austin, 

 in Travis County, Texas. Seven of these rats 

 were cinnamon in color, the others, obviously 

 the wild type, were gray or brownish. The 

 cinnamon color is restricted to the back and 

 sides of the head and body, and is due to the 

 presence of yellow pigment in the outer ends 

 of the hairs, the pigment of the hair base 

 probably being chocolate. In the type and 

 mutant specimens the fur on the ventral sur- 

 face, from the chin to the base of the tail, is 

 snow white, the hairs being white from the 

 tip to the base. 



We attempted to keep these rats in the lab- 

 oratory, but after a few weeks they began to 

 die. I then instructed one of our assistants to 

 preserve the skins. Some of these were later 

 sent to Professor W. E. Castle, who showed 

 them to Dr. G. M. Allen. Dr. Allen identifies 

 the species as the roof rat, Mus alexandrinus. 



We were anxious to establish a stock of the 

 cinnamon rat for genetic studies, and through 

 the kindness of Miss Hill and her family, I 

 was able to visit the farm on July 6. During 

 the day we captured 215 rats. Upon examina- 

 tion, the rats proved to be of three varieties, 

 Mus norvegicuSj Mus alexandrinus, and the 

 cinnamon mutant. We took 61 specimens of 

 the common Norway, 138 of the type of roof 

 rat, and 16 of the cinnamon. Undoubtedly 

 some of the 138 specimens of the roof rat are 

 heterozygotes. We were fortunate enough to 

 capture a mother and four young in one nest. 

 Three of the litter are like the brownish-gray 

 mother, and the third a typical cinnamon. 



The interesting point concerning the discov- 

 ery of this cinnamon rat relates to its origin. 

 When and how did it happen to appear on the 

 Hill farm? With a view of answering these 

 questions, I made a careful study of the con- 

 ditions on the farm. The farm buildings 

 where the rats are found are close together and 



