146 



POPULAR SCIENCE NEWS. 



[October, 1889. 



as a blanket or heavy cloth does. By arrang- 

 ing a paper tube, or gutter, over a candle 

 flame, a stream of carbonic dioxide may be 

 poured down upon it like water, and will 

 extinguish it as quickly. 



Carbonic dioxide is very easily prepared. 

 In the laboratory it is made by the action of 

 hydrochloric acid upon marble, but it can be 

 made just as well by placing some baking or 

 washing soda in a large bottle or pitcher, 

 pouring on vinegar, and covering the top 

 loosely with a piece of paper or cardboard 



Fig. 2. 



till the air is displaced and the vessel is filled. 

 The gas may then be directly poured out, as 

 described in the preceding experiments, tak- 

 ing care, of course, not to spill the liquid at 

 the bottom. A still easier way of procuring 

 the gas is by mixing baking-powder or seid- 

 litz powders with water only. 



These, and all other similar experiments, 

 require a little care and practice, but are so 

 simple that anyone can soon learn to perform 

 them, and are as instructive as the more bril- 

 liant ones, which require complicated appara- 

 tus and much skill in manipulation. 



THE LIMITS OF VISION. 



If the surface of the earth were a plane:, or 

 flat surface, an object would always be visible 

 upon it at a distance only limited by its size, 

 or the strength of eyesight of" the observer, 

 and the power of his telescopes. We know, 

 however, that the surface of the earth is 

 spherical, and, therefore, no matter what the 

 size of an object, at a certain distance — de- 

 pending upon its height and that of the 

 observer above the surface of the earth — it 

 will become invisible, the convexity of the 

 earth rising up like a wall between them. 



It is often a matter of interest and import- 

 ance to know how far one can see from any 

 given height, or, conversely, how far one 



must be above the earth to see an object at a 

 given distance. The exact calculation of 

 these figures would require the use of very 

 complex formula;, but, for practical use, two 

 very simple rules will suffice : 



The distance in miles at ■which an object 

 upon tJie surface of the earth is visible, is 

 equal to the square root of one and a half 

 times the height of the observer in feet 

 above the stirface, and, conversely, 



The height in feet to which an observer 

 must be placed to see a distant object, is 

 eq/tal to two-thirds the square of the dis- 

 tance in yniles. 



For instance : The observer is in the rig- 

 ging of a ship, one hundred feet above the 

 water, how far distant is the horizon .' that is, 

 how far could an object floating in the water 

 be visible before being hidden by the convex- 

 ity of the earth .? One and a half times one 

 hundred is one hundred and fifty, and the 

 square root of one hundred and fifty is, 

 approximately, twelve and a half, therefore 

 the horizon is twelve and a half miles dist^t. 

 As the deck of smaller vessels, like pleasure 

 \achts, is rarely more than ten feet above the 

 water, it follows that the limit of vision from 

 that point is less than foiu" miles in every 

 direction. 



An illustration of the second rule may be 

 given as follows : A building is thirty-three 

 miles away ; how high a hill must one climb 

 in order to be able to see it } As the square 

 of the distance equals i ,089, and two-thirds 

 of that number equals 736, it follows that we 

 must climb a hill 726 feet high before we are 

 able to see the building, even with the most 

 powerful telescope. 



Usually, however, the height of the object, 

 as well as that of the observer, must be taken 

 into consideration, but this simply requires 

 the duplication of the problem. For instance : 

 The Washington Monument is 552 feet high ; 

 at what height must an observer fifty miles 

 away be in order to see the top of it .' Sup- 

 posing the observer to stand upon the ground, 

 we find by the first rule that he could just see 

 the top 29 miles away, and to overcome the 

 remaining 21 miles, due to the convexity of 

 the earth, he would, by rule second, have to 

 climb to a height of 294 feet. 



Or, suppose a sea-captain standing on the 

 deck of his vessel, 30 feet above the water, 

 can just see the light of a certain lighthouse, 

 which he knows to be 100 feet high ; how far 

 is he from it.' By using rule first for both 

 heights, and adding the results together, we 

 find that the light is 19 miles distant from the 

 ship, — a piece of information which might be 

 of the highest value. Similar problems will 

 occur to everyone. 



If we apply similar calculations to the 

 Eiffel Tower, the highest artificial structure 

 in the world, we obtain some interesting 

 results. Assuming the height to be just 



1,000 feet, we find that, standing at the top, 

 we enjoy a circle of vision bounded by a 

 horizon 39 miles distant, and that, if another 

 similar tower should ever be erected, it could 

 be placed over 78 miles away before the rays 

 of the electric lights on their summits would 

 be eclipsed by the intervening earth. From the 

 summit of Mt. Everest in the Himalayas 

 (27,000 feet) one could see nearly 200 miles, 

 provided the air was clear enough, which 

 would rarely be the case. 



[Orij^inal in The Popu'ar Science 2^twt.] 



MODERN ARCHAEOLOGICAL DISCOVERIES 



BY JOSEPH WALLACE. 



How would the ancient historian and archicolo- 

 gist Hekateus feel today in the presence of our 

 galaxy of scientists, who have shed a halo of light 

 on ancient history and archajologj, when he showed 

 so much vanity and bragging in his day as to claim 

 relationship with a divine grandsire in the sixteenth 

 degree, and provoke the taciturn Hierodule of The- 

 ban to lead him into the inner sanctuary — that 

 grand hall — where one after another of the three 

 hundred and forty-five colossal wooden statues of 

 earth-born high priests were found in unbroken 

 series, who bequeathed from father to son the sacred 

 dignity.' 



The arch;eological discoveries in Palestine, Egypt, 

 and Assyria, the present century, are as wonderful 

 as they are valuable. No alone to ethnical history 

 are they valuable, but also to sacred literature, as 

 they clear up all past and existing doubts in Bibli- 

 cal history. A summary account of the modern 

 discoveries in these countries — which were first in 

 civilization, first in the sciences, and first in the 

 arts — is es.sential to a proper appreciation of the 

 long, patient, and arduous labors of the archaeolo- 

 gists, besides furnishing a key to the long locked 

 and hidden secrets, which the rise and fall of dynas- 

 ties, continual wars, and exodus of the people had 

 sealed in characters which defied alike the stern 

 hand of time to efface, and the uninitiated in cunei- 

 form writings to solve. 



The Hebrews and Assyrians have one common 

 origin ; their forefa.thers shared the same soil for a 

 long time, and followed the same mode of life. 

 Towards the last days of their history, the two na- 

 tions found themselves united under Nebuchadnez- 

 zar. Between the two extreme periods of voluntary 

 separation and forced reunion, the sons of Heber 

 and the sons of Assur led at first an independent 

 existence, but always preserved, so to speak, the 

 imprint of the same family education. The ethnic 

 character of the ancient Assyrians, like that of the 

 Chaldeans, was, in former times, a matter of contro- 

 versy ; and, when nothing was known of the original 

 language of the people, beyond the names of certain 

 kings, princes, and generals, believed to have be- 

 longed to the race, it was difficult to arrive at any 

 determinate conclusion on the subject. "The inge- 

 nuity of the etymologists displayed itself," says 

 Rawlinson, the great Egyptologist, "in suggesting 

 derivations for the words Jn question, which are 

 sometimes absurd, sometimes plausible, but never 

 more than very doubtful conjectures. No sound 

 historical critic could be content to base apositi\e 

 view on any such unstable foundation, and nothing 

 remained but to decide the controversy on the lin- 

 guistic considerations." 



Various grounds existed on which it was felt 

 that a conclusion could be drawn. The scriptu- 

 ral genealogies connected Assur with Arum, Heber, 

 and Joktan. the allowed progenitors of the Arama'- 

 a»s and Syrians, the Israelites or Hebrews, and the 



