ASTRONOMY ON MONT BLANC. 181 



files of porters, and the workers of the windlass, which were jjlaced 

 from point to point to aid in moving the heavier pieces over the 

 dangerous declivities. When the material was finally in place the 

 carpenters from Meudon began its erection, and, favored by a fort- 

 night of calm weather, they were able to complete their work on the 

 8th of September. M. Janssen, eager to see the Avork, resolved to 

 imdertake another ascension, in which he availed himself of the 

 windlasses this time to drag his sledge. He reached the top on the 

 11th, about midday, and remained there four days, occupied princi- 

 pally with observations of the solar spectrum, formed by a fine 

 Rowland grating. 



Janssen undertook another ascent in 1895, with the principal 

 object of making sure that all the parts of the large telescope of 

 33 centimeters aperture for the observatory, had come up in good 

 condition, and were in shape to pass the winter without injury. 

 This telescope is mounted in connection with a polar siderostat, so 

 that its axis is parallel with the axis of the earth and receives the 

 light reflected from the siderostat mirror. Both the mirror, of 60 

 centimeters diameter, and the objective were presented by the Henry 

 brothers. All the adjustments are controlled from the observer's 

 station, who thus has no need to move about, and may remain in 

 a closed room kept at a comfortable temperature. This beautiful 

 instrument, whose mechanical joarts were constructed by Gautier, 

 was mounted not without some difficulty in 1896. M. Janssen also 

 inspected the registering meteorograph, which had been installed in 

 1894, but had stopped. This instrument Avas constructed by M. 

 Jules Richard, and is driven by a weight of 90 kilograms, which 

 falls 5 or 6 meters in eight months and keeps in motion a pendulum 

 which regulates the motion of the registering mechanism. There is 

 continuous registration of the barometric pressure, temperature, 

 humidity, and velocity and direction of the wind. It jDroved that 

 the apparatus lacked stability, and it ran after being given a support 

 independent of the flooring, but the instrument has never gone 

 very regularly. Another meteorograph, also designed to go eight 

 months without rewinding, has been installed at Grands Mulcts. 



The problem of securing a very long running meteorograph suit- 

 able to be placed on a high mountain as a substitute for observations 

 during the bad season is one of great delicacy, which requires further 

 trials. M. Janssen is much interested in it and has proposed a new 

 form, in which the rotation and fall of a registering cylinder is 

 brougth about by its own weight. JNI. Poncet, professor of horology 

 at the college of Cluses, is engaged witli the construction of a meteoro- 

 graph of this kind. Up to the present time no registering meteoro- 

 graph has been run more than eight or nine months. 



