Mr. De la Rue on the Total Solar Eclipse of July 18, 1860. 69 



has been satisfactorily demonstrated by a more extended series of 

 experiments, and the rate of expansion of superheated steam is 

 shown to be almost identical with that of air and other permanent 

 gases, if calculated at temperatures not too close to the maximum 

 temperature of saturation. 



" On a New Method of Approximation applicable to Elliptic and 

 Ultra-elliptic Functions." By Charles W. Merrifield, Esq., F.R.S. 



April 10. — Major-General Sabine, President, in the Chair. 



"On the Total Solar Eclipse of July 18, 1860, observed at Riva- 

 bellosa, near Miranda de Ebro, in Spain." — The Bakerian Lecture. 

 By Warren De la Rue, Esq., F.R.S. 



The Lecturer gave an account of the more interesting phenomena 

 of the eclipse, and of the methods employed in observing and 

 recording them; the details of his observations being given in an 

 elaborate Paper bearing the above title. The Lecture was illustrated 

 by a great number of diagrams and models. The photographic 

 images of the eclipse were projected on a screen by means of the 

 electric lamp, and some of the more striking phenomena were imi- 

 tated by apparatus contrived for that purpose. 



The following is an abstract of the Paper : — 



The author, for some time previous to the organization of the 

 Astronomer Royal's expedition to Spain, had contemplated making 

 an attempt to photograph the phenomena of the total eclipse of 

 July 18th, 1860, but as soon as he was informed of the Astronomer 

 Royal's views he agreed to join his party, now known as the 

 Himalaya Expedition, from the name of Her Majesty's ship which 

 conveyed the astronomers composing it to Spain. He attributes 

 much of the success of his operations to the admirable arrange- 

 ments of Professor Airy in England, and to those concerted with Mr. 

 Vignoles in Spain ; for he was able in consequence greatly to increase 

 the extent of his preparations, and to convey a complete temporary 

 observatory fitted up with all the numerous requirements which are 

 essential in astronomical photography. Besides himself, his party 

 consisted of Mr. Beckley of the Kew Observatory, Mr. Reynolds 

 (now Mr. De la Rue's private assistant), Mr. Downes, and Mr. E. 

 Beck, and subsequently the late Mr. S. Clark. The author expresses 

 himself greatly indebted to these gentlemen for their most efficient 

 assistance. 



The party took up their station at a village called Rivabellosa, 

 situated near the town of Miranda de Ebro ; the site selected was a 

 thrashing-floor, on which the observatory was erected. 



The instruments employed consisted of the Kew heliograph, for 

 the photographic records ; an achromatic telescope, by Dallmeyer, 

 mounted on a sort of alt-azimuth stand contrived by the Astronomer 

 Royal, which permitted of an equatorial movement by the ingeni- 

 ously arranged joint action of two racked radius bars. To this tele- 

 scope the author fitted a diagonal eyepiece of his own contrivance, 

 which allowed of the use of reflexion from plain glass in the first 



