638 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



cate the existence of some fixed law by wliich heavy bodies may be so 

 finely divided that they may remain suspended between the atoms or mole- 

 cules of liquids or gases? 



Several processes for extracting gold wore adverted to, and facts pre- 

 sented wliich the speaker was not aware had been fully discussed at previous 

 meetings of the Association. 



It was stated, in reply, that the late Prof Ren wick had explained how 

 gold eluded the grasp of the washer when in the form of a snlphuret, and 

 why the tailings, after being exposed to the air for several years, would 

 yield gold on a second washing. 



Prof. Everett said the process for dissolving gold quartz by means of 

 hydrofluoric acid was not economical, on account of the cost of making 

 the decomposition of fluor-spar. 



Color-Blindness. 



Dr. Rowell had placed on the wall some blue-colored cards, having upon 

 each one large and one small red spot; he wished to show how much the 

 power to distinguish colors varied in a mixed audience. It will be found 

 that the small spot will appear blue when the spectator has removed a cer- 

 tain distance. This distance is different for nearly every spectator. 



Mr. John E. Gavit said this experiment did not illustrate what is com- 

 monly known as color-blindness, for the person thus defective cannot dis- 

 tinguish certain colors when they are placed quite near the eyes. Distance 

 has nothing to do with color-blindness. Since different colored lights have 

 been used as signals on railroads and in light-houses on the sea coast, the 

 subject has assumed great importance. He remembered that in crossing 

 the Atlantic in 1846, this subject was the topic of conversation as the ship 

 came in sight of a certain light which was known to be red, yet to no two 

 persons did this light appear to be of the same color. The number of per- 

 sons deficient in the power to distinguish all the colors is much larger than 

 is generally supposed. At his request Mr. Garvey, the Secretary, read the 

 following extract on this subject from The Popular Science Review: " From 

 the calculations of various authors that one persoa out of every fifteen is 

 color-blind, and from the investigations of the late Dr. Wilson upon 1,154 

 persons at Edinburgh, made in 1852-3, we gather that 1 in 55 confounded 

 red with green, 1 in 60 confounded brown with green, 1 in 46 confounded 

 blue with green; hence that 1 in every 18 had this imperfection. Profes- 

 sor Siebeek found 5 out of 40 youths in the upper class in a school at Ber- 

 lin color-blind. Professor Provost thinks it occurs on an average in 1 in 

 20 persons; and Wartmann, whose investigations almost exhaust the sub- 

 ject, thinks this estimate is not exaggerated. M. Lubeck rejects this con- 

 clusion as unsound, from the observations being made in England and 

 Germany, where blue is the prevailing color of the eyes; and it is a ques" 

 tion with him whether it occurs so frequently in persons the i7'ides-co\or of 

 whose eyes is black or hazel. In answer to this it seems the great ma- 

 jority of cases examined by Wartmann had black irides." 



Mr. G. Bartlett said the terrible railroad accident at Norwalk, Conn., 

 several years since, was caused by the engineer's mistake in the signal that 

 the draw of the bridge was open. A gentleman who had this defect in 



