August 22, 1902.] 



SCIENCE. 



317 



A few examples may make the subject more 

 clear. 



If (p = 72°,a = 36°-thenp~2,r = 2,k = i, 

 and all the images are visible to an eye any- 

 where between the two mirrors. 



If (J=.72°, a=10°;;) = 3, r = 2, i = 5, 

 but only three of the five images will be visible 

 to an eye placed within 25° of the mirror 

 furthest from P,,. 



li ^ = 55°, a = 25° ; p = 3, r = 3, * = 6. 



If <l> — 55°, a = 10°;p = 4, r = 3, k = 7. 

 If the eye be placed within the angle /5 only 

 five of the seven images are visible. This is 

 the case shown in the figure. 



It is interesting to observe the results ex- 

 perimentally and see one of the images dis- 

 appear or merge into another at critical angles. 

 For p=55°, a critical case is given by 

 a=15°. 



MoRTOs' GiTHENS Lloyd. 



Randal Morgan Laboratory of Physics, 

 University of Pennsylvania. 



THE PLANET EROS. 

 The planet Eros, as we noted last week, was 

 rediscovered on the morning of August 2 by 

 Dr. Chas. J. Ling with the twenty inch re- 

 ■ f ractor of the Chamberlin Observatory at Uni- 

 versity Park, Colo. It was found pretty close 

 to the place derived from an ephemeris com- 

 puted by Miss Mary Clark Traylor. But it 

 was estimated to be considerably brighter than 

 had been expected. In view of the fact that 

 the law of its variability is unknown the re- 

 sults of photometric measures will be awaited 

 with interest. As Eros is now low in the east 

 when the morning twilight begins, and is ad- 

 vancing in right ascension nearly as fast as 

 the sun, it will not be an easy object for some 

 months to come. The position on August 11 

 at I5I1 25m 19s Univ. Park M. T. was 



AE 51 36m 35.03s. 

 Decl.-|-31° 56' 17.7". 



Hole on August 12, it was voted to transfer 

 the laboratory and its equipment to the Car- 

 negie Institution. . This action was taken after 

 it had been stated to the members of the cor- 

 poration that the executive committee of the 

 Carnegie Institution would recommend to the 

 trustees that the laboratory should be accepted, 

 that its debts should be paid, that new build- 

 ings should be erected, that $20,000 a year 

 should be allowed for maintenance and that 

 the scientific management should rest as here- 

 _tofore with the naturalists of the country. A 

 motion that a three fourths vote of the mem- 

 bers present be required for the transfer of 

 the property of the corporation was defeated 

 by a vote of 32 to 19. It was voted without 

 dissent that an account of the action of the 

 corporation be made public. 



. THE MARINE BIOLOGICAL LABORATORY 

 AND THE CARNEGIE INSTITUTION. 

 At a meeting of the corporation of the Ma- 

 rine Biological Laboratory held at Woods 



SCIENTIFIC NOTES AND NEWS. 



Dr. N. L. Britton sailed for England on 

 Aug-ust 16, where he will complete some in- 

 vestigations iipon American Carices and Cras- 

 sulacece which will be issued as the first parts 

 of the ' Systematic Botany of ISTorth America ' 

 to be published by the New York Botanical 

 Garden. Dr. MacDougal will be acting direc- 

 tor of the garden during his absence. 



Professor J. E. Wolff, of the U. S. Geolog- 

 ical Survey, is continuing the investigation of 

 the areal and structural geology in the crystal- 

 line areas of New Jersey, in cooperation with 

 the state geologist. 



Dr. Robert Bell, of the Geological Survey 

 of Canada, has been engaged in the geological 

 survey of Baffin Land, which he finds to have 

 an area of about 300,000 square miles, making 

 it the largest island with the exception of Aus- 

 tralia _ and Greenland. The results of Dr. 

 Bell's explorations are to be presented to the 

 Eoyal GeogTaphical Society. 



Mr. Borchgrevink, the Norwegian explorer, 

 has taken out naturalization papers, so as to 

 Americanize the Antarctic expedition he is 

 planning under the auspices of the National 

 Geographical Society. 



Medical exchanges state that the committee 

 of the Liverpool School of Tropical Medicine 

 is making arrangements to enable Major Ron- 



