Zi)t popular Science jSetMS 



AND 



BOSTON JOURNAL OF CHEMISTRY. 



Volume XXII. 



BOSTON, DECEMBER, 1888. 



Number 12. 



CONTENTS. 



Familiar Sciekce. — The KeceDt Volcanic Explosion in 



Japan 173 



Our Neighbor across the Way 173 



The History and Mystery of a Dew-Drop 174 



Paris Letter 175 



The Number of the Stars 176 



Spiders' Webs 178 



8cientiiic Brevities 176 



Practical Chemistry and the Arts. — The Rare Metals, 177 



Caricature Photographs 177 



Optical Illusions 178 



Laboratory Notes 178 



Industrial Memoranda 178 



Home, Farm, and Gabdeh. — The Chemistry of Bread- 



Matting 179 



The Mandrake 179 



A New Method of Potato Culture 179 



How to Tell a Horse's Age 180 



Some Immense Cakes 180 



Oleanings 180 



Editorial. — On the Ultimate Causes of Action in Animals. 181 



The British Association at Bath 182 



Meteorology for October, 1888 183 



.Astronomical Phenomena for December, 1888 184 



Another Tree.Pruner 184 



Questions and Answers 184 



Literary Notes 184 



Medicine and Pharmacy. — Minor Ailments 185 



Climatology and Health-Resorls 185 



Treatment of Snake. Bite 186 



Teeth as Conservators of Nerve Force 186 



Monthly Summary of Medical Progress 187 



Degeneration of the Human Teeth 188 



Humors 188 



PuBLisHBRg' Column 188 



JFamtltai; ^tirtue. 



THE RECENT VOLCANIC EXPLOSION IN 



JAPAN. 



The past few years have been remarkable 

 for the number of destructive volcanic erup- 



tent, was converted into "a land of fire." 

 The latest volcanic catastrophe is reported 

 from Japan, where, on the loth of last Juh, a 

 large portion of Mount Bandai was broken 

 up into dust and fragments, and scattered over 

 the adjoining country. The accompanying 

 illustration (Fig. 1) shows the appearance of 

 a formerly fertile valley after it was filled with 

 d4bris from the explosion, and is from a pho- 

 tograph taken by Mr. W. K. Burton of Tokio, 

 who was sent by the Japanese government to 

 investigate the explosion, and whose report is 

 published in the British Journal of Photogra- 

 phy. Fig. 2 is a diagram showing the part of 

 the mountain destroyed by the explosion. 



This phenomenon is properly spoken of as 

 an explosion rather than as a volcanic erup- 



. Fio. 1. 



lions in various parts of the world. The ex- 

 plosion of Krakatoa, where an entire island 

 was blown into the aij-, occurred only five 

 years ago ; and a short time afterwards a tract 

 of country in New Zealand, several miles in ex- 



tion. There was no trace of lava or igneous 

 phenomena of anj- kind. It was simply an 

 immense explosion like that of a steam-boiler, 

 where the overlying mountain was torn apart 

 by the force of the steam generated by the 

 terrestrial heat. Clouds of steam escaped 

 from the ground in the vicinity of the moun- 

 tain for some time after the explosion ; and 

 when the pressure was first relieved by the 

 destruction of the mountain, torrents of water 

 and mud rushed down the valle3-s, causing 

 immense loss of life and damage to property. 

 In some respects this explosion is similar to 

 the eruption which destroyed Pompeii, when 

 a large part of Mount Vesuvius was destroyed ; 

 but in that instance the usual igneous phenom- 

 ena were more evident, although the loss of 

 life was apparently' much less. The dwellers 

 at the foot of Vesuvius had ample warning of 

 the eruption before it took place, but the un- 

 fortunate Japanese appear to have liad no 

 opportunity to escape the catastrophe. 



[Original in The Popular Science A'«o«.] 



OUR NEIGHBOR ACROSS THE WAY. 



BY PROFESSOR C. A. YOUNG. 



The planet Mars occupies in the solar system 

 the orbit next outside the Earth's, and at times 

 comes nearer to us than any other heavenly body, 

 excepting only the Moon and the planet Venus, or 

 now and then a stray comet. But when Venus is 

 nearest the Earth, her illuminated surface is 

 turned away ; so that the Moon alone offers better 

 opportunities for telescopic examination than does 



Mars when, at its opposition, it is for a season the 

 chief ornanient of the evening sky. 



The reader must not, however, imagine that, 

 because the planet is then nearer than other heav- 

 enly bodies, its distance is really comparable with 

 any geographical distances on the earth's surface. 

 Even under the most favorable circumstances, the 

 distance is never less than about 36,000,000 miles, 

 which is about 150 times that of the Moon, and a 

 full century's railway journey for a " celestial lim- 

 ited," running forty miles an hour, without stops. 

 Even with a magnifying power of a thousand, 

 which is about the highest that can be advanta- 

 geously used on any but the very largest telescopes, 

 and under exceptional circumstances, the planet is 

 still optically fully 36,000 miles away, and shows 

 in the field of view a disk about 6J° in diameter, 

 upon which the smallest objects visible would need 

 to be 25 or 30 miles across. A rather powerful 

 field-glass, with a magnifying power of six or seven, 

 would bring the Moon as near. 



It is only about once in fifteen years that Mars 

 comes as near as even 36,000,000 miles. Its orbit 

 is so eccentric, that the interval between it and the 

 orbit of the Earth varies all the way from 36,000,- 

 000 miles to 61 ,000,000 ; and it is only now and then 

 that, as the two planets circle round in their respec- 

 tive tracks, the passing point is where the tracks 

 come nearest. The last instance of a very close 

 approach was in 1877; the next will be in 1892. 



Mars is much smaller than the Earth, its diam- 

 eter being only about 4,200 miles ; its bulk there- 

 fore is only about one-seventh, and its surface 

 about three-tenths, of the Earth's. 



By means of the motion of its swift little moons, 

 it is easy to a.scertain that its " mass" (i.e., the quan- 

 tity of matter it contains) is somewhat less than one- 

 ninth of the Earth's, and consequently its density 

 is only three-fourths, and its superficial gravity just 

 about three-eighths, of the Earth's ; i e., a body 

 which at the Earth's surface weighs 100 pounds, 

 would weigh only 38 pounds there, and a force 

 which here would project a body to an elevation of 

 100 feet, would throw it there to a height of 265. 

 This is a point of considerable importance in con- 

 sidering the physical conditions of the planet. 



When examined by the telescope under favor- 

 able conditions. Mars is a very pretty and interest- 

 ing object. It shows a ruddy disk, which, for 

 .some not certainly known reason, is much brighter 

 at the edge than near the centre ; in this respect 

 resembling Mercury, Venus, and the Moon, but 

 standing in marked contrast with Jupiter and Sat- 

 urn. According to Zollner, the " albedo," or 

 reflecting power, of its surface is about twenty-six 

 per cent; that is to say, it reflects about twenty -six 

 per cent of all the light which falls upon it, — 

 about as much as ordinary sand. This is consider- 

 ably higher than the albedo of either Mercury or 

 the Moon, but only about halt that of Venus or 

 any of the major planets. 



Just at the time of opposition the disk is, of 

 course, perfectly circular; but at other times it is 

 more or less " gibbous," like the moon a day or two 

 from the full. It varies greatly in apparent size 

 according to the changing distance of the planet, 

 which ranges all the way from 250,000,000 miles 

 to 36,000,000. 



