POPULAR MISCELLANY. 



121 



ther to the deceptive and dangerous char- 

 acter of the defects, I have, in the course 

 of my experiments, found a number of per- 

 sons who were unable to distinguish between 

 the primary colors at night, while their per- 

 ception or sensation of color by daylight 

 was apparently perfect. Again, I have found 

 another anomaly which, until it has been 

 more thoroughly investigated, and the real 

 causes that produce it are understood, I 

 shall designate as a form of color-blindness, 

 although I am in doubt myself as to its de- 

 pendence upon any of the principles that 

 enter into that defect ; this is an inability 

 to distinguish between or to recognize the 

 primary colors at certain distances, varying 

 more or less in individuals. This was found 

 to be the most difficult of all defects to de- 

 tect in the various cases I have examined, 

 amounting to some nine or ten, in the regu- 

 lar course of my business as optician during 

 the past three years. I have found no two 

 of them at all alike except in general re- 

 sults. 



" I have kept records of various acci- 

 dents that have occurred, both upon land 

 and water, during the past few years, and 

 I have gathered such information about 

 some of them as I could get outside of of- 

 ficial sources often I was unable to get 

 any of any value, but I am convinced be- 

 yond a doubt that a large proportion of 

 them could have been traced to this defect 

 for a correct solution as to the primary 

 causes of the accident. The query has 

 been made, that if these defects in their 

 various forms are as numerous and of such 

 a dangerous character as has been shown, 

 how can we account for such a compara- 

 tively small number of accidents occurring 

 which might be charged to them ? I have 

 attributed it to the high average intelligence 

 and acquired cautiousness of engineers and 

 pilots as a class. They have become so ac- 

 customed to be on the lookout for danger 

 that their suspicions are easily aroused, 

 which creates a sort of instinct that governs 

 their actions, and they do not recognize but 

 that their perceptions are correct." 



Sewer-bnilding. The general principles 

 of sewer-building are, says the Polytechnic 

 Journal, that each day's influx should be 

 promptly passed out by natural flow or 



flushing, and not allowed to deposit sedi- 

 ment. The alignment should be good, es- 

 pecially at the bottom ; the descent should 

 be uniform, and the interior surface smooth, 

 so as to reduce friction and not to cause 

 clogging; the walls should be absolutely 

 impervious, and the suction such as will 

 cause the most rapid possible flow, with a 

 minimum of sewage. Rapid flow being es- 

 sential, smooth interior walls should be pro- 

 vided; mortar projecting from the joints 

 of a brick sewer markedly impedes the 

 flow and arrests putrefiable matter. A flat- 

 bottomed sewer is the worst form as regards 

 the velocity of the flow ; a circular bottom 

 is better; an egged-shaped section, with the 

 point downward, permits of a minimum cur- 

 rent flushing and cleansing the bottom. In 

 brick sewers the mortar, constantly moist, 

 must sooner of later succumb to the disinte- 

 grating action of the matters passed through 

 it, and the whole line gradually passes into 

 the condition of a sieve, allowing the liquid 

 portions of the sewage to pass through it 

 and to saturate the subsoil, but retaining 

 the solids. From the consequent saturation 

 of the soil result contagious fevers. Hence 

 vitrified clay pipes are now almost univer- 

 sally employed. The " slip " glazing applied 

 to these pipes resists the severest chemical 

 action of sewage-water. The " slip " glaze 

 is produced by dipping the unbaked clay 

 into a mixture of " slip-clay " or Albany- 

 earth and water, which, under a white heat 

 continued from twelve to thirty hours, pro- 

 duces a vitreous and very durable silicious 

 surface upon the wares. 



Remarkable Laud - Slides. Bear-Tooth 

 Mountain is one of the most prominent land- 

 marks in Northern Montana ; it is plainly 

 visible from Helena, thirty miles distant. 

 It presents, or rather used to present, the 

 appearance of two great tusks rising hun- 

 dreds of feet above the general contour of the 

 mountains. One of these tusks, the smaller 

 one, which was fully five hundred feet high, 

 three hundred feet in circumference at the 

 base, and one hundred and fifty feet at the 

 top, was recently dislodged from its place 

 and precipitated into the valley below. A 

 few weeks since, according to the Helena 

 Independent, a party of hunters chasing 

 game several miles north of the Bear Tooth 



