540 



NATURE 



[April 7, 1898 



of Europe, the perusal of these chapters should prove 

 useful ; and so should the description of the various great 

 centres of population on the coast, in the Yangtze valley 

 and Pekin. 



Not the least interesting of the photographs is that 

 which, by the courtesy of the publishers, we are able to 

 give here. The illustration shows two ancient astro- 

 nomical instruments of purely Chinese construction, 

 which stand on the walls of Pekin, with mstruments 

 dating from the thirteenth century, and others con- 

 structed for the Chinese Government by the Jesuit 

 missionaries of the seventeenth century. The circles of 



comparatively few astronomical observers, that means of 

 communication were slow, and that the importance of 

 recording these objects as precisely as possible had not 

 been recognised. 



The present is perhaps an appropriate period to refer to 

 this subject, for it was in 1798, just a century ago, that 

 the first systematic attempt was made (by Brandes at 

 Leipzic, and Benzenberg at Dusseldorf ) to determine the 

 heights of meteors. Schroter had in 1 795 seen a shooting- 

 star (in his reflecting telescope of 20 feet focus), the 

 height of which he estimated at more than four millions 

 of miles 1 Brandes and Benzenberg, however, found 



A.ncienl Chinese Astronomical Instruments. 



the instruments of the thirteenth century are divided into 

 365^ degrees to correspond to the days of the year, each 

 degree being subdivided into hundredths, but the later 

 instruments have their circles divided into 360 degrees. 



THE HEIGHTS OF METEORS. 



IT is perhaps surprising that the heights of meteors, and 

 especially of that class known as fireballs, were not 

 determined with any accuracy until the near approach of 

 the present century. It is true that a few individual 

 attempts were made in this direction but, considering the 

 large number of brilliant meteors which appear every 

 year, it is curious that some systematic attempts were not 

 made at a much earlier date in this direction. It must, 

 however, be remembered that many years ago there were 



NO. 1484, VOL. 57] 



from 22 meteors which they mutually observed in 1798, 

 heights varying between 6 and 140 miles. Brandes in- 

 stituted some further observations in 1823, and of 62 

 meteors available for calculation 55 were found to have 

 heights between 30 and 70 miles. On August 10, 1838, 

 M. Wartmann, at Geneva, followed up Brandes's inquiries, 

 and derived the average height of the meteors seen on 

 that occasion as 550 miles, and their velocity 240 miles a 

 second. These values, compared with modern observ- 

 ations, were far less accurate than Brandes's earlier ones. 

 It is not proposed in this paper to deal fully with the 

 average heights of meteors, for that has been discussed 

 by several authorities. The values are about 76 and 51 

 miles respectively for the mean elevations at appearance 

 and disappearance. In the case of fireballs, however, 

 they penetrate much deeper into our atmosphere than 



