Apeil 9, 1897.] 



SCIENCE. 



585 



DISCUSSION AND C0BBE8P0NDENCE. 



DIFFRACTION OP X-RAYS OBTAINED BY A NEW 

 FORM OF CATHODE DISCHARGE. 



To THE Editor of Science : Will you allow 

 me to publish a very brief statement concerning 

 some work which is now in progress on the 

 diffraction of X-rays. The trouble has been in 

 obtaining a sufficiently intense source to give 

 diffraction bands with the very narrow slits that 

 must be used. After considerable experiment- 

 ing I have found a new method of producing 

 the rays, by which the intensity of radiation 

 per unit of area of radiating surface is from ten 

 to twenty times as powerful as in the best focus 

 tubes. A ' total radiation ' equal to the large 

 focus tubes has not yet been obtained. The 

 rays are produced by an arc-like discharge be- 

 tween two very small beads of platinum in a 

 high vacuum. The discharge bulb is only about 

 an inch in diameter, while the radiation (which 

 comes from an area about the size of a pinhead) 

 is strong enough to show the bones in the fore- 

 arm. The 'arc' appears to be a new form of 

 cathode discharge and can only be produced 

 under peculiar conditions. I am now using a 

 tube with a platinum slit 1 mm. wide, mounted 

 within the bulb at a distance of 2 mm. from the 

 radiating bead. The second slit of variable 

 width is placed at a distance of 10 cm. from 

 the first and the photographic plate at dis- 

 tances varying from 10 to 30 cm. from this. 



The images of the slit on the plate show a 

 distinct dark line on each edge, which I can 

 only explain on the supposition that interfer- 

 ence occurs. The plate is at too great a dis- 

 tance from the slit for such an effect to be pro- 

 duced by reflection of the rays from the edges. 

 Images of fine wires show similar phenomena. 



As yet I have not succeeded in getting a 

 maximum of the second order, possibly because 

 of under exposure of the plates. The details 

 of the work will appear shortly in Wiedemann's 

 Annalen and The Physical Review. I am under 

 great obligation to Professor Cross for his kind- 

 ness in placing at my disposal the facilities of 

 the physical laboratory of the Massachusetts 

 Institute of Technology. 



E. W. Wood. 



Jamaica Plains, Mass., March 31st. 



THE height and THE VELOCITY OF THE FLIGHT' 

 OF A FLOCK OF GEESE MIGRATING NORTH- 

 WARD. 



During the three days ending March 22d 

 numerous flocks of geese were seen migrating 

 northward, or rather northeastward, since they 

 were following the general trend of the coast 

 line, which, in New England, is nearly north- 

 eastward north of Cape Cod. On the morning 

 of March 22d, while Mr. A. E. Sweetland and 

 I were measuring clouds, at the ends of a base 

 line 1178.4 meters in length, extending from 

 the Blue Hill Meteorological Observatory to 

 the base of Blue Hill, we succeeded in measur- 

 ing, with our cloud theodolites, the height and 

 the velocity of flight of one of these flocks of 

 geese. So rapid is the velocity of flight that 

 the flock was visible to the observers only 

 about two minutes, but during that time two 

 sets of measurements, were taken with the 

 theodolites on the leader of the flock. The 

 first measurements, at 8.49 a. m. , were accu- 

 rately taken at the Observatory station, but 

 were only approximate at the other station. 

 The second measurements, at 8.50 a. m. , were 

 accurate and simultaneous at both stations. 

 Using the second set of observations at both 

 stations for the height and the two sets of ob- 

 servations at the observatory station for the 

 velocity, the calculations gave the height as 

 905 feet above the Neponset River valley, or 

 960 feet above sea level, and the velocity of 

 flight as 44.3 miles an hour. The direction of 

 flight was from southwest to northeast. 



The self-recording instruments at Blue Hill 

 Observatory, 615 feet above the river valley, 

 showed that the wind at the time of the meas- 

 urements was from the west-northwest with a 

 velocity of eight miles an hour. 



The height calculated from the first set of ob- 

 servations at the two stations was 928 feet above 

 the river valley. This result, though not con- 

 sidered strictly accurate, serves as a good check 

 on the adopted value which is given above. 



On a previous occasion as described in Science 

 of January 1st, p. 26, we found a flock of ducks 

 flying from the northeast at a height of 958 feet 

 with a velocity of 47.8 miles an hour. The 

 close agreement between the two results is sug- 



