POPULAR MISCELLANY. 



837 



angulation was extended over about 12,000 

 square miles. Materials were collected for 

 a topographical map of the Yellowstone 

 Park, on the scale of one mile to an inch. 

 Its geology was studied minutely. A peak 

 of the Wind Kiver range, named Fremont's 

 Peak, was found to be over 14,000 feet in 

 height above the sea; no trace could be 

 seen of the presence of man on its summit 

 at any time. Three glaciers were discov- 

 ered on the east side of the Wind River 

 Mountains. The object of again surveying 

 the Yellowstone Park was to bring it under 

 the system of triangulation, which has been 

 very successfully employed in Colorado, and 

 to make the entire work uniform. All the 

 old hot-spring basins were resurveyed and 

 mapped, soundings and temperatures of sev- 

 eral thousand hot springs were made, and 

 the action of the geysers carefully studied. 

 Over fifty fine photographic views were ob- 

 tained of the bowls and other curious or- 

 namental details of the Hot Springs. 



The Personal Equation,— One of the 



principal defects of " our primary mathe- 

 matical instrument," the human mind itself 

 with its organic apparatus, is very clearly 

 pointed out by W. Mattieu Williams. This de- 

 fect makes itself apparent in certain astro- 

 nomical observations, when the observer has 

 to note the moment at which a star appears 

 to touch the wire or wires stretched across 

 the field of a telescope. The old way of 

 doing this was to look at a clock as the 

 star approaches the wire, count the beats 

 of the clock, and then note at which beat 

 or fraction of the beat the transit of the 

 wire occurs. Despite the apparent simpli- 

 city of this operation there is no human 

 being whose eye, ear, and internal nervous 

 apparatus of perception and volition are 

 sufficiently perfect to perform it accurately. 

 None of us either sees, hears, or feels in- 

 stantaneously. The sensation has to be 

 transmitted from the external organ of 

 sense to the nervous center, and the re- 

 sponse has to be transmitted outward. 

 These operations involve time. Nor is that 

 all : they require a different length of time 

 for different persons, different constitutions. 

 Thus in the same observatory there may be 

 three assistants. A, B, and C, and they are 

 tested by making a number of correspond- 



ing observations. In every case it will be 

 found that A is say a quarter of a second 

 ahead of B, and B half a second ahead of 

 C. What is to be done ? If all erred 

 alike — if all observers required just half a 

 second to collect their sensations of sight 

 and hearing, and to bring them to bear 

 upon the same perception, then by setting 

 the clock half a second ahead of the true 

 time, the needed correction would be made. 

 But, failing this, some personal standard of 

 comparison must be taken, and the observ- 

 ers' rated to this standard like chronome- 

 ters. This is done in observatories, and 

 the result is called the " personal equation " 

 of the individual observer. And not only 

 has the personal equation of each observer 

 to be determined on his entrance upon his 

 duties, but it demands periodical revision, 

 for it varies with age and constitutional 

 conditions. 



t'sc of the Balloon in Arctic Explora- 

 tion. — In a paper read before the London 

 Aeronautical Society, Mr. Brearey, its secre- 

 tary, advocated the employment of balloons 

 in polar exploration. Referrring to the last 

 English polar expedition, Mr. Brearey said 

 that, instead of a seventy days' journey to 

 accomplish about seventy miles, at a fearful 

 cost of life and suffering, consequent on hav- 

 ing to drag over ice hummocks sleds con- 

 taining provisions, the whole of the stores 

 could have been conveyed over the heads of 

 the explorers, and the men holding the ropes 

 of this floating observatory would have 

 been assisted by the upward tendency of 

 the balloon. The question is, Would the 

 daily consumption of stores compensate the 

 leakage of gas ? and its answer is found in 

 Beaumont's history of the balloon as em- 

 ployed in the United States war of the re- 

 bellion. He writes that " the balloon when 

 inflated can, unless in very windy weather, 

 be very readily carried. Twenty-five or 

 thirty men lay hold of cords attached to 

 the ring and march along, allowing the ma- 

 chine to rise only sufficiently to clear any 

 obstacle." He had frequently seen it car- 

 ried thus without the least difficulty. As 

 for the leakage of gas, by the use of proper 

 varnish it might be so checked that at the 

 end of a fortnight the balloon could make 

 an ascent without being replenished. Re- 



