ynne 20, 1872] 



NATURE 



M5 



Dr. Williamson said, that those who were there present 

 ought not to separate without some expression of the plea- 

 sure that they had felt on listening to so learned, va't. and 

 eloquent a discourse, tieating as it did of a most d'flicult 

 and miportant problem. There was scarcely anything of 

 greater moment in the scientific education of youth than 

 the rightly setting before them those wonderful transfor- 

 mations of matter which it is the province of chemistry to 

 explain. These great and growing truth?, for, as the 

 lecturer had said, they were growing truths, should be set 

 before youth in such a manner as to form a coherent 

 whole. He hoped to study this masterly discourse with 

 profit and delight, and would now propose a vote of 

 thanks to his illustrious colleague for the honour which 

 he Lad done them in delivering to them the Faraday 

 lecture. 



Prof. Tyndall said he had heard the discourse with deep 

 interest, for it showed that the lecturer knew the impor- 

 tance of a teacher's vocation, and that his province was 

 not merely to communicate knowl dge, but to do it in 

 such a manner as to arouse an interest in and love of the 

 subject in the pupil by presenting it in its proper relations. 

 He would have welcomed the lecturer to that Institution, 

 even had he come to tear in pieces the notions which he 

 cherished regarding atoms and molecules ; how pleasant 

 it was then to find such a broad agreement between their 

 views. The chemist cannot halt at ecjuivalent propor- 

 tions — he must ask himself whence they arise, and the in- 

 evitable answer is some form of the atomic theory. This 

 theory,however,cannotbe confined to chemical phenomena. 

 The motions of those atoms and molecules underlie all our 

 explanations of the physical cause of light and he.it, 

 and it is already taking up the field of magnetism and 

 electricity. Consider, for example, the heat of gases, 

 both as regards the motion of translation of the mole- 

 cules which produce temperature, and the motions of 

 rotation and vibration of their constituent atoms, which, 

 though they do not express themselves as temperature, 

 constitute a portion of the heat. Clausius has shown that 

 even in the simplest gases nearly two-fifths of the whole 

 heat is due to these internal motions ; while in gases of 

 complex molecular constitution which condense on com- 

 bining, the ratio of the total heat to the heat of tempera- 

 ture is still greater. The experiments of Regnault, which 

 show that the specific heat of a perfect gas at a constant 

 volume is constant, proves, as Clausius has shown, that 

 the one kind of motion is proportional to the others. 



The lecturer had also referred to atoms of the same kind 

 combining together, so that, free oxygen and free hydrogen 

 being considered as composed of molecules each con- 

 taining a pair of atoms, has certainly simplified the re- 

 sults. But it must not be forgotten that this combination 

 of like atoms is widely different from that of unlike 

 atoms. The union of oxygen with o.Kygen or nitrogen 

 with nitrogen produces no such effects upon the lumini- 

 ferous ether as the union of oxygen with nitrogen. With 

 the same quantity of matter the amount of vis viva sent 

 forth as radiant heat may be augmented a thousandfold, 

 perhaps a millionfold, by the act of diverse combination. 

 This act seems to carry with it a condensation of the ether 

 to a dense atmosphere around the atoms. Had a cannon 

 the power of gathering round itself a dense atomsphere, it 

 would send fotth a greater amount of I'is vh'a as sound. 

 A gun fired at Chamouni may be heard upon Mont lUanc, 

 while the same gun fired on Mont Blanc may not be heard 

 at Chamouni, because the air on which the concussion 

 takes place is denser in the one case than in the other. 

 In the same way the diverse atoms vibrating in the denser 

 atmosphere formed on combination show their vast 

 superiority as radiators over like atoms which, except in 

 such special cases as ozone, cSic, are incompetent to pro- 

 duce a similar condensation. The speaker then asked 

 them to echo the resolution so well put to the meeting by 

 Prof. Williamson. 



THE OBSERVATORY ON MOUAT VESUVIUS 



WHILE the scientific world and his own countrymen 

 are rivals in doing honour to Prof. Palmicri for his 

 zeal in remaining at his post in spite of all danger, it may 

 be interesting to examine in some detail the work done at 

 the Observatory of Mount Vesuvius. We know wonder- 

 fully little about the origin and mutual dependence of 

 volcanic phenomena. This is due to a want of accurate 

 observations. For the complete investigation we require 

 first to know at what dates earthquakes and eruptions 

 occur at different parts of the earth. Next we must have 

 observations of the direction and exact hour at which a 

 wave of disturbance passes different places whose posi- 

 tions arc known. This gives us the velocity of the wave, 

 and helps to determine the position, under the earth's 

 surface, of the centre of disturbance ; or, if a wave be 

 propagated over the sea, we obtain a means of estimating 

 the average depth of the intervening ocean ; for the velo- 

 city of a wave increases with the depth of the sea . This 

 method gives one of the best determinations we possess 

 of the depth of the Pacific Ocean. But beyond this we 

 must have observations made systematically at some 

 place subject to earthcjuakes and volcanic eruptions. No 

 place in Europe is more suitable for this than the neigh- 

 bourhood of Mount Vesuvius ; and it was for such obser- 

 vations that an Observatory was established there. 



Everyone knows that Mount Vesuvius consists of a 

 great cone of lava and ashes, at the top of w-hich is the 

 great crater. On the northern side, separated from it by 

 the deep valley called the Atrio del Cavallo, rises the 

 precipitous and semicircular Monte Somma. This once 

 formed the crater of the volcano, and the present cone 

 seems to have been formed inside that great crater at the 

 time when Pompeii was overwhelmed. On a spur of rock, 

 a mile or two in length, running down from the Atrio del 

 Cavallo, the Observatory is placed. It is close to the 

 well-known " Hermitage," or half-way house, in the ascent 

 of the mountain. Being raised on this ridge above the 

 surrounding country, it is comparatively safe from the 

 molten lava that flows at times on either side of it. 



The building itself is handsome ; in fact it is to be re- 

 gretted that so much money should have been devoted to 

 the masonry instead of to additional instruments. On the 

 ground floor are the inhabited rooms, all scantily furnished ; 

 but the pursuers of science cannot always expect bodily 

 comfoit. On the first floor we find the Museum, with a 

 fine collection of minerals found on the mountain. Per- 

 haps it may be as well here to correct a common mistake 

 as to the nature of the yellow substance found about the 

 craters, whose brilliant colours remind one so much of the 

 Solfatara. This substance is not sulphur, but copper. 

 The most interesting objects in the Museum are the 

 "fumerolles," or smoke-holes. Occasionally at the end of 

 an eruption you may see at the bottom of the crater a 

 small cone of lava, with a hole in its top, thiough which 

 the steam pours with a hissing noise like a wave breaking 

 on a pebbly beach, or like a blast furnace, or as Pliny has 

 it, like the grinding of a saw ; the intensity of the sound 

 varying with your position. These small cones arc the 

 fumerolles ; they are a foot or two high ; and Palmieri 

 has actually had several of these natural chimneys cut off 

 and transported to the Museum. 



We now pass on to the Observing Room. There are 

 solid piers carried up from the ground to support the in- 

 struments. First comes the elegant seismograph for the 

 automatic registration of earthquake shocks. The object 

 of the instrument is twofold : first to measure the direc- 

 tion and intensity of a shock ; and, second, to write down 

 a history of the earthquake. The shock may be either 

 vertical or horizontal, or partly vertical and partly horizon- 

 tal. For the vertical shocks a fine metallic point is suspended 

 by a coil of wire over a cup of mercury. The coil of wire 

 acts as a spring, and the slightest upward motion of the 



