Mabch 6, 1896.] 



SCIENCE. 



357 



of cloud on a scale of to 10, and the chance 

 in percentages of its occurrence are as follows : 

 August 8th, 8 P. M. August 9tli, 8 A. M. 



^TCd"' Chance. -^"SoSd."' ^^--'^-■ 



10 45.5 10 45.5 



8 13.7 9 9.1 



.7 4.6 8 4.6 



5 4.5 7 9.1 



3 9.1 6 4.5 



2 4.5 4 4.6 



18.2 3 4.5 



2 9.1 



9.1 



100.1 100.1 



"InVadso there is a telegraph station, and 

 time signals are to be had from the observatory 

 in Christiania. The latitude and longitude have 

 been determined with all possible accuracy. 

 Sydvaranger lies on the south side of the Var- 

 angerfjord and Elvenes is the name of the posting 

 station. Vardo, lying on the north side, is not to 

 ber ecommended, having too often fog or clouded 

 sky. In the interior of Finmarken the sun is 

 lower than at Varangerfjord." 



Although the astronomical conditions of low 

 altitude of sun and short totality are not good, 

 yet the meteorological conditions just noted 

 compare favorably with those of stations in 

 Japan, where the eclipse occurs later in the day 

 and totality lasts longer. As a basis of com- 

 parison for the chance of clear weather, it may be 

 stated that here at Blue Hill, Mass., near the 

 coast, at 8 A. M. in August the average fre- 

 quency of cloudy weather (sky 8 to 10 tenths 

 covered) is 50.0 per cent, and the average fre- 

 quency of clear weather (sky to 2 tenths cov- 

 ered) is 32.3 per cent. 



A. Lawrence Eotch. 

 Blue Hill MeteoeoloqicalObseevatoey, Feb- 

 ruary 20, 1896. 



THE EONTGEN EAYS. 



The following fact regarding the X-rays of 

 Rontgen may be of interest: 



I have found that it is possible to obtain a 

 photographic image by these rays using a ' pin- 

 hole camera,' having the aperture pierced in a 

 piece of sheet lead backed with aluminum. 

 The Crookes tube was illuminated, by discharges 

 from a Thomson high-frequency coil. The 



photographs taken in this way show very dis- 

 tinctly the two electrodes, while the glass bulb, 

 which appeared to be brightly illuminated to 

 the eye, is scarcely perceptible. It would ap- 

 'pear from this that nearly, if not all, the so- 

 called X-rays proceed directly from the elec- 

 trodes of the tube and not from the glass where 

 this is acted on by the cathode-rays. It like- 

 wise aftbrds further illustration of the recti- 

 linear motion of the X-rays. Experiments are 

 in progress with a broken current and also to 

 study the effect of a magnetic field. 



Previous observation had shown that the 

 photographic effects were produced equally 

 whether the cathode rays impinged upon the 

 glass or upon other phosphorescent material (e. 

 g., arragonite) within the tube. It has also 

 been noticed in experiments in this laboratory 

 that the appearance of the tube to the eye af- 

 fords no criterion of its eflSciency in producing 

 the X-rays ; tubes showing but little fluores- 

 cence of the glass composing them often giving 

 admirable photographic effects, which in some 

 cases are obtainable even from a low-vacuum 

 Geissler tube. But the rays producing photo- 

 graphic effects always appear to produce strong 

 flourescent effects on platino-cyanide of ba- 

 rium, so that the fluorescence of this affords an 

 indication of the photographic efiiciency of the 

 radiations emitted from the tube. 



Ealph E. Laweence. 



Massachusetts Institute of Technology, 

 Boston, Febmary 26, 1896. 



EONTGEN EAYS PEESENT IN f3UNLIGHT. 



In the course of a series of experiments on 

 the so-called Eontgen or X-rays, the undersigned 

 have secured evidence of the presence of these 

 rays in sunlight, and have been able to reproduce 

 many of the phenomena ascribed to the X-rays, 

 without the use of vacuum tubes or any other 

 source of light or energy than direct sunlight. 



Dr. Egbert was led on February 22d to place 

 in a photographer's printing frame, an ordinary 

 sensitive plate (Seed's No. 26), upon which was 

 superimposed a positive lantern slide, and on 

 this a shield of aluminium; which -was then ex- 

 posed to the direct rays of the sun for two hours, 

 . and the plate developed, when it was found 

 that the aluminium shield had been ti-ansparent 



