September 19, 1902.] 



SCIENCE. 



475 



fined, although the boundary between the two 

 was somewhat indistinct. There was, how- 

 ever, no question whatever about the existence 

 of the definite colors. 



The appearance of the bow may, perhaps, be 

 better understood by reference to the accom- 

 panying figure in which the X.Z-plane repre- 

 sents the ground, while the observer is standing 

 at the origin, his head being at H. The shad- 

 ow of the observer's head would then fall upon 

 the plane at XZ at H', and the bow appeared 

 on the ground between the feet of the observer 

 and the shadow of his head, and extended 

 on either side in the manner indicated in the 

 sketch. 



Assuming the simple explanation of the 

 rainbow to apply in this case, the figure of the 

 bow would be given by the intersection of the 

 XZ-plane with the 42° cone (red rays), gener- 

 ated by the rotation of the line HP about 

 8HH' as an axis, at an angle of 21°. The 

 form of the bow is, of course, dependent upon 

 the altitude of the sun. With the sun at the 

 horizon, and for altitudes up to 21°, the figure 

 would be a hyperbola; at 21°, it would be a 

 parabola. At altitudes of the sun above 21°, 

 we would have an ellipse, becoming a circle at 

 the zenith with its center at the origin of co- 

 ordinates. 



The phenomenon was readily observed on the 

 morning succeeding the first observations, but 

 three days later, when another heavy dew ap- 

 peared, no trace of the bow could be seen. 

 During this time the grass had grown consid- 

 erably, and the irregularity in height appeared 

 to prevent the reflection of a sufiicient amount 

 of light. The existence of the bow has not 

 yet been noted on any lawn on which the grass 

 has attained considerable size. 



Lyman J. Briggs. 



Washington, D. C. 



X0TE8 ON INORGANIC CHEMISTRY. 



CENSUS BULLETIN OF CHEMICALS AND ALLIED 



PRODUCTS. 



Tins 'Bulletin,' prepared by Professor 

 Charles E. Monroe and Dr. T. M. Chatard,, 

 which has just been issued, is extremely inter- 

 esting reading and is full of valuable informa- 

 tion. It is in effect a brief review of th& 

 chemical progress of this country in the last 

 decade, with glimpses of the progress else- 

 where, when this would seem to have a bear- 

 ing upon possible future development here. 

 Thus are treated at some length the catalytic 

 production of sulfuric acid, the manufacture 

 of soda from the natural soda of the West, 

 wood distillation, fertilizers, explosives, and 

 particularly chemical substances produced by 

 the aid of electricity. It is interesting to note 

 that the value of the principal products re- 

 ported in this 'Bulletin' is $221,217,217 as com- 

 pared with $163,547,685 reported in the census 

 of 1890. Except in the potash industry, which 

 is insignificant, there has been an increase in 

 every department, but hardly as great as might 

 have been looked for, considering the greatly 

 increased attention given to the application of 

 science to industry. Possibly this is more 

 readily understood from the statistics of chem- 

 ists employed in the establishments treated of 

 in this report. From this it appears that the 

 total number so employed in the United States 

 is 276, about half the number employed by six 

 coal-tar color finns of Germany. The largest 

 number employed in any one industry is 52, 

 in paints and varnishes. Those in the coal- 

 tar products number 7, to which should prob- 



