136 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



in a collected form, the best materials which yet exist for the 

 identification of lines, and for the reduction of fresh determi- 

 nations to wave-lengths. Rep. Brit. Assoc., 1873, 250. 



ADVANTAGEOUS CONSTRUCTION OF THE SPECTROSCOPE. 



In some remarks upon the optics of the spectroscope, Mr. 

 Sorby states that in the construction of a spectroscope the 

 eye-piece should be of as long a focus as possible, so as to 

 cause all the rays to enter the eye. All magnifying beyond 

 this means loss of brilliancy ; and if the spectrum appears 

 insufficiently large, an increase in the size of the collimating 

 and telescope lenses, together with the prisms, or an in- 

 crease in the number of prisms, should be made, until the 

 spectrum appears large enough to suit the requirements of 

 the observer. 12 A, X., 469. 



abbe's refractometer. 



The new instrument devised lately by Professor E. Abbe, 

 of Jena, for the determination of the index of refraction of 

 any transparent body, has received high encomiums, and 

 promises to be of use in all optical researches. In principle 

 it is, we understand, based upon the property of total reflec- 

 tion of light. Two similar right-angled prisms are so fixed 

 that their hypothenuses are parallel and a slight distance 

 apart. Between them is placed the liquid to be examined, 

 and by measuring the angle through which this combination 

 must be turned in order to secure the total reflection of a 

 ray of light, we have the means of directly determining the 

 index of refraction. In order to employ white light, and 

 annul the indistinctness caused by the dispersion of light, 

 a compensator is introduced, based upon a combination of 

 flint and ground-glass prisms, and it is stated by Professor 

 Waltenhofer that the execution of measurements with this 

 instrument leaves nothing to be desired as regards rapidity, 

 elegance, and accuracv. Technische Blatter. 1874, 106. 



THE CAUSE OF THE LUMINOSITY AND NON-LUMINOSITY OF 



FLAMES. 



It has been ascertained that if nitrogen, hydrochloric acid, 

 or carbon dioxide be passed into the flame of a Bunsen burn- 

 er, it becomes non-luminous; but when any such mixture 



