696 



SCIENCE. 



[N. S. Vol. XIV. No. 357. 



SHORTER ARTICLES. 

 CENTROID OF A QUADRANGLE. 



So far as I can ascertain, the following con- 

 struction is new. If it be old, it would seem 

 worth while to recall attention to it. 



To find the centroid of any quadrangle A, 

 B, C, D, divide each side into three equal parts, 

 and draw lines through adjacent points of 

 division, as indicated in the figure. It is easy 

 to prove that the new figure is a parallelogram, 

 the center of inertia of which coincides with 

 the center of inertia of the original quadrangle, 

 both occurring at the intersection of the 

 diagonals of the parallelogram. The areas of 

 the two figures difier. 



In that admirable digest, ' Des Ingenieurs 

 Taschenbuch herausgegi:?ben vom Verein Hiitte,' 

 17th edition, no less than thirteen constructions 

 are given for finding the centroid of quad- 

 rangular figures. It would seem to me that 

 one convenient and easily memorized construc- 

 tion should suSice, and that the space thus 

 saved should be otherwise utilized. 



G. F. B. 



EFFECT OP DIMINISHED AIR-PRESSURE ON 

 THE PULSE. 



To THE Editor of Science : In a recent trip 

 to the summit of Pikes Peak I made some ob- 

 servations on the rate of my pulse which show 

 a rapid increase of beat corresponding with a 

 rapid decrease of pressure. The ascent was 

 made from Manitou on the cog railway, and as 

 I was comfortably seated all the way and spent 

 most of the time looking from the car window, 

 the influence of exercise on the results was elim- 

 inated, because there was no change in this re- 

 spect. The train stopped after each climb of 

 about 2,000 feet to take on water and at these 



stops I took the rate of my pulse. The heights 

 of the different points are taken from a guide 

 furnished by the railway company, and these 

 with the number of observed pulse beats per 

 minute are given in the accompanying table. 



Kate of Pulse pee Minute. 



It is seen that the pulse increased regularly 

 to the summit and decreased to the same 

 amount on the way down. When near the 

 summit I asked a lady sitting near me to give 

 me her pulse rate and she found it the same as 

 my own, namely, 92 per minute. 



The average rate of my pulse at the same 

 time of the day (near mid-day) at sea level is 

 about 75. 



The ascent was made on September 1, and the 

 time occupied in the ascent and return was 

 about four hours, between noon and 4 p. M. 

 About an hour and a half was taken for the 

 ascent and about an hour and a half for the 

 descent, leaving about an hour for remaining on 

 the summit. 



I did not notice any diflSculty of breathing 

 while on the summit of the Peak, or any sen- 

 sations markedly different from those experi- 

 enced at sea level. 



On the day of my visit the Peak was be- 

 tween two strata of cumulus clouds. One was 

 evidently formed over the plateau to the west 

 of the Peak and floated over some distance 

 above the summit. The other stratum was 

 formed over the plains to the east and was far 

 below the summit of the Peak. 



Henry Helm Clayton. 



Blue Hill Observatory, 

 October 7, 1901. 



NOTES ON INORGANIC CHEMISTRY. 



The nature of an antimony salt described in 



1882 by Setterberg has lately been cleared up 



by Wells and Metzger, writing in the American 



Chemical Journal. This salt was formed by the 



