I87I.] 



(io7) 



PROGRESS IN PHYSICS, 



(Including Light, Heat, Electricity, Meteorology). 



LIGHT. 



Mr. C. B. Boyd has devised a novel form of telescope. It consists of a 

 plane speculum, having an equatorial motion, which reflects, an object to a 

 conclave speculum at a distance ; this in turn reflects the image to the eye- 

 piece situated behind the plane mirror; a hole in the centre of the latter 

 allowing this to be done. This arrangement brings the mirror and eye-piece 

 close to the observer, while, at the same time, it enables one to have a very 

 long telescope, without any great extra expense, for an observatory : it 

 combines, in fact, both observatory and telescope in one construction. A 

 thirty-foot telescope needs an observatory that will cost £"10,000 ; while in 

 this arrangement the observatory proper needs only be sufficient to cover the 

 equatorial, the instrument itself being 50, 100, or. 500 feet long. 



In a letter from Professor Young, of Dartmouth College, N.H., we learn 

 that he has succeeded in obtaining photographs of protuberances on the sun's 

 limb. They were obtained by attaching a small camera to the eye-piece of the 

 telescope and opening the slit somewhat v/idely, working through the hydrogen 

 line near G. Three-and-a-half minutes' exposure was required, and the double- 

 headed form of the prominence is evident. 



Professor Young has also designed a new form of spectroscope for 

 observations upon the solar spots and protuberances, a detailed description of 

 which appeared in the " Chemical News," vol. xxii., p. 277. Although the 

 instrument has the dispersive power of 13 prisms of heavy flint, each with an 

 angle of 55 , it weighs less than 15 pounds, and measures only 15 inches in 

 length, 8 in breadth, and 4^ in height. The collimator and observing 

 telescope have each an aperture of |ths of an inch, and a focal length of 

 7 inches. The light from the slit, after passing the collimator, is transmitted 

 through the lower portion of a train of six prisms of heavy flint glass, each 

 2,\ inches high, and having, as stated above, a refracting angle of 55 . A 

 seventh half-prism follows, and to the back of this is cemented a right-angled 

 prism, by which, after two total reflections, the light is sent back through the 

 upper part of the same train of prisms, until it reaches the observing-telescope. 

 This is placed directly above the collimator, and firmly attached to it. A 

 diagonal eye-piece brings the rays to the eye in a convenient position for 

 observation. 



Observations of the Solar Protuberances. — With this instrument Professor 

 Young has observed about forty different prominences. Fig. n represents a 



small one, which was observed upon 



Fig. 11. 



the E. limb of the sun on September 

 14th, about 4.30 p.m. From the 

 point marked a, which was very 

 brilliant, a small fragment detached 

 itself and rose towards a', enlarging 

 in size and growing fainter as it rose. 

 It disappeared (from faintness) in 

 about twelve and a half minutes, at 

 a distance of 2' 30" above the limb 

 of the sun, as determined by the 

 time, 8*5", which, was occupied by 

 the intervening space in passing over 

 the slit of the spectroscope. Allowing 

 for the obliquity of the motion to the 

 parallel of declination, the length of 



