656 



SCIENCE. 



[N. S. Vol. III. No. 70. 



difficulty of securing photographs of all 

 kinds of clouds in all weather is very great, 

 and the cost of the work much more for the 

 same number of individual observations. 

 The international classification of cloud 

 forms has been issued, and it will be 

 adopted by the Weather Bureau and go 

 into operation July 1, 1896, throughout the 

 service. Suitable instructions and illustra- 

 tive forms have been prepared for the ob- 

 servers, with which they are to become 

 familiar before the date mentioned. The 

 atlas of cloud forms issued by the Commit- 

 tee is now ready for distribution, and may 

 be purchased of M. Teisserenc de Bort, Bu- 

 reau Central Meteorologique, 176, rue de 

 I'Universite, Paris, France. 



Besides the observations with theodolites 

 and photogrammeters for the actual heights 

 and velocity of motion of clouds at the pri- 

 mary stations, a number of secondary sta- 

 tions for the relative motions, and the other 

 available data, will be established in each 

 country. In the United States there will 

 probably be ten such stations under the im- 

 mediate control of the Weather Bureau, 

 equipped with nephoscopes for the obser- 

 vations. It is very desirable that the net- 

 work of the stations be made as complete 

 as possible in all parts of the country, and 

 it is hoped that this opportunity for co- 

 operation may be embraced by other persons 

 willing to do some valuable scientific work. 

 The colleges might profitably instruct their 

 students in such observations at a very 

 moderate expense. A first-class ngpho- 

 scope can be made for twenty dollars, and 

 serviceable ones at lower rates. The obser- 

 vations would require half an hour's work 

 three times a day, between 8-9 a. m., 1-2 

 p. m., 5-6 p. m. The Weather Bureau will 

 furnish suitable instructions to observers, 

 and will aid them as far as possible in ex- 

 plaining the very simple computations that 

 would be needed to prepare the obser- 

 vations for final discussion. 



There are many forms of nephoscopes in 

 use, but the one devised by Prof. Marvin, of 

 the Weather Bureau, seems to be especially 

 well adapted to the requirements. A de- 

 scription of it will be found in the January 

 number of the Weather Review. It may 

 be said in this place that its best feature is 

 the device for keeping the sighting knob ex- 

 actly twelve centimeters above the mirror 

 in every possible position, so that the unit 

 of height becomes 1000 meters, and the 

 velocity in meters per second at that height 

 'is just one third the number of millimeters 

 passed over by the image in 25 seconds. 

 This makes the computations very easy, 

 and when the height of the cloud level is 

 known from the theodolite work, the actual 

 velocity is obtained by simply identifying 

 the cloud observed from its form as belong- 

 ing to such a level. The mean of a large 

 numberof observations gives a true velocity. 

 The base line at Washington is about 1360 

 meters long, one end on the Weather Bureau 

 building, and the other on the War, State 

 and Navy building. The ratios of velocity 

 by the theodolites and nephoscopes at this 

 station, in the diiierent cloud levels, gives 

 the means of using other nephoscope ob- 

 servations, provided the naming of the 

 cloud forms is carefully done. 



The ultimate problem is to obtain the 

 coordinate velocities of the several com- 

 ponents in the general circulation, and the 

 relation that these have to the cyclonic 

 circulations which depend upon them. The 

 importance of these solutions to the art of 

 forecasting, and the fact that voluntary ob- 

 servations made in widely separated parts 

 of the United States are needed as contri- 

 butions to the network, together with the 

 simplicity that pertains to nephoscope work, 

 induces the hope that some interested in 

 the physics of the air may take up the task 

 of cooperation." 



Frank H. Bigelow. 



Washington. D. C. 



