Jan. 27, 1876] 



NATURE 



251 



the inner cone, is screwed a light wooden beam, f, hori- 

 zontally. Through the beam and lid passes a perforation 

 for receiving the thermometer. At a little distance from 

 the beam, /, and at the same height, there is a fixed 

 pulley, g, over which is passed a cord with a scale at its 

 pendant extremity, while the other end is attached to the 

 end of one arm of the beam (the second arm of the beam 

 acts as counter weight). When the driving machine is 



put in action, the cones rub together, and the outer cone 

 tends to carry the inner one and its beam round with it 

 in the direction of rotation. With a certain weight in the 

 scale, the horizontal part of the cord will form with the 

 axis of the beam a right angle. From the length of the 

 beam-arm, the amount of weighting, and the number of 

 rotations, may be deduced the work that is transformed 

 into heat ; and from the water value of the calorimeter. 



and the increase of its temperature, can be reckoned the 

 quantity of heat produced. 



From twenty-eight experiments (in which the amount 

 of heat radiated from the calorimeter was taken into 

 account), the average value obtained for the mechanical 

 equivalent of heat was 425 "2, with a mean error ± 5'4. 

 A second series of experiments was made, with the arm 

 of the beam in any position with reference to the cord. 

 A simple arrangement — wooden triangle with arc-division 

 — ser\'ed for measuring the angle which the axis of the 



beam-arm formed with its normal position (in which it 

 forms a right angle with the cord). From the observed 

 values of this angle, and from the quantities already 

 referred to, the number obtained for the mechanical equi- 

 valent of heat was 4267, with a mean error ± 5 "9. 



The apparatus is especially to be recommended for 

 lecture-experiments, because the method of experimenting 

 is extremely simple, and the carrying out of the experi- 

 ment takes very little time. A single experiment occupies 

 30-60". S. W. 



A' 



THE PHYSICAL OBSERVATORY ON THE 

 PIC DU MIDI 



T a recent sitting of the Paris Academy of Sciences 

 ^ M. Ch. Sainte-Claire Deville made a communication? 

 with reference to the proposed Physical Observatory on the 

 Pic du Midi, in the PjTenees. He referred to the 

 increasing importance of meteorolog>', and to its manifold 

 extensions and development in recent years, and to the 

 growing necessity of establishing numerous fixed stations 

 at as high an altitude as is practicable. This has already 

 been done to a considerable extent in India, in America, 

 and in some parts of Europe ; in France, as we have 

 already intimated, the Puy de Dome Observatory is 

 nearly completed. M. Deville then referred to the im- 

 portance of having a station on the Pyrenees, and to the 

 di.Ticulty of choosing a suitable site. The Pic du Midi de 

 Bigorre, however, unites in itself all the most favourable 

 circumstances. Situated towards the middle of the chain 



of the Pyrenees which receive directly the shock of the 

 Atlantic storms, the Pic du Midi stands out from the 

 general crest, and rises to a height of 2,877 metres, 

 only 527 metres below the highest summit of the chain. 

 It commands a magnificent and extensive panoramic 

 view, and is easily accessible from various points. From 

 the sixteenth century downwards it has attracted tee 

 attention of men of science, and during the last and th- 

 present century a considerable number of notable ob 

 servers have resorted to the Pic for the purpose of carrying 

 on observations. Darcet, in 1786, obtained from Philippe 

 d'Orleans the promise of 80,000 francs to found an obser- 

 vatory on the mountain, but the political events which 

 rapidly succeeded prevented the scheme from being carried 

 out. Even then a small hut existed on the spot where 

 the Commission, charged by the Ramond * Society with 

 carrj'ing out the present scheme, have built another ; the 

 former had been built by Vidal and Reboul, who in 

 1786-7 sur\'eyed the Pic. Ramond, in the early part of 



