692 



SCIENCE. 



[N. S. Vol. I. No. 25. 



But the destruction of the Lemmings 

 after reaching the lowlands is onlj^ in small 

 part due to these enemies. " The most 

 active factor in their extermination," says 

 Dr. Collett, " appears to be infectious dis- 

 eases, which invariably occur whenever a 

 species of animal has multiplied in excess 

 of its natural numbers." 



Not only do the Lemmings themselves 

 die of disease; but they are believed to 

 cause serious disease among the human 

 population. This belief has been current 

 in Norway from time immemorial and was 

 published by Ziegler more than 350 years 

 ago. Dr. Collett states that during Lem- 

 ming years all running water is contam- 

 inated by the decaying excrement. " To 

 this may be added the dead animals, which 

 ■will be found lying scattered about in great 

 numbers, and which, during hot summers, 

 become quickly decomposed. The rain 

 carries the putrid matter on to the nearest 

 watercourse, whence it m.akes its way to 

 wells, and becomes mixed with the drinking 

 water of the inhabitants. 



" During some great prolific years, definite 

 forms of sickness have appeared in certain 

 of the overrun districts, and the people have 

 given these the name of ' Lemming Fever,' 

 as they presumed that they were connected 

 with the appearance of these animals." 



After citing medical testimony and de- 

 scribing the disease. Dr. Collett concludes: 

 " Lemming fever is thus a disease which, 

 in its phenomena, is related to scarlet fever. 

 Its origin is regarded, both by medical men 

 and the populace, as having a certain con- 

 nection with the appearance of the swarms 

 of Lemmings and the pollution of water by 

 their putrifjdng carcasses and dung during 

 dry summers." 



Dr. Collett's treatise on the Habits and 

 iligrations of the Lemming in Norivay is re- 

 plete with interest from beginning to end 

 and must long remain the standard authority 

 on the subject. C. H. M. 



NOTES AND NEWS. 

 ASTRONOMY. 



The London Times gives the following, 

 accounts of recent lectures before the Royal 

 Institution and of the last meeting of the 

 British Astronomical Association : 



Dr. ^Y. Huggins, F. E. S., gave the sec- 

 ond of his course of lectures on the insti-u- 

 ments and methods of spectroscopic astron- 

 omji-, at the Royal Institution, on Maj' 30th. 

 He dealt with the more complex instrument 

 wliich is placed at the eye-end of the tele- 

 scope so that the images of the stars fall 

 upon its slit. The important question of 

 its efiicienoy was connected, the lecturer 

 said, with its power to break up the spec- 

 trum into as many parts as possible. This 

 power of separation was fixed by certain 

 conditions — the linear length of the spec- 

 trum, its dispersion, and the resolving 

 power of the prism. The latter, which was 

 independent of dispensive power, was gov- 

 erned by the size of the prism, hence larger 

 prisms have greater resolving power. But 

 the use of larger prisms in astronomical 

 work entailed certain disadvantages, such 

 as increased weight and cost, and difficulty 

 of obtaining glass of uniform quality. It 

 was therefore fortunately possible to get the 

 results of large prisms by passing the beam 

 through several smaller ones, though the 

 loss of light bj'' absorption and reflection 

 from the faces of the prisms was very serious. 

 An alternative way of obtaining a spectrum 

 was to use a diffraction grating, which we 

 owed to the experiments Fraunhofer made 

 to discover whether the lines of the spec- 

 trum were due to interference of light. 

 His original gratings were made by winding 

 wire in a screw-thread round a piece of 

 glass ; ultimately he adopted the plan of 

 ruling the lines on glass with a diamond 

 point. Great advances were made by 

 Eutherfurd, whose machine cut lines to the 

 number of 17,000 to an inch, and by Row- 

 land. There is, however, but little to choose 



