152 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



ing the temperature and the direction-current at any partic- 

 ular depth in the ocean. It consists of a brass box, hermetical- 

 ly closed, and having attached to it an apparatus resembling a 

 vane or rudder. Within this box a thermometer and a mag- 

 netic needle are contained, behind each of which is placed sen- 

 sitive photographic paper, and in front of each of which is a 

 small nitrogen vacuum tube. The box contains also a small 

 induction coil. When the apparatus is lowered to the re- 

 quired depth, the rudder causes it to take a direction paral- 

 lel to the current there existing, and hence a definite direc- 

 tion with reference to the needle within. The thermometer 

 soon acquires the temperature of the water outside, and be- 

 comes stationary. At this instant an electric current is sent 

 to the box, which, by means of the induction coil inside, lights 

 up the little nitrogen tube, the violet light of which, photo- 

 graphically very intense, prints, in about three minutes, the 

 position of the needle and the height of the mercury column 

 upon the prepared paper. The current is then intermitted, 

 the apparatus raised, the photographic tracing fixed, exam- 

 ined, and placed upon record. 3 B, Sej^t. 3, 1874, 6. 



DISPERSIOX OF LIGHT BY PEISMS. 



Dr. Eugene Block attempts, in his Inaugural Dissertation, 

 to make some additions to the theory of the refraction of 

 light passing through systems of prisms. He says with ap- 

 parent correctness in his preface that the many occasions 

 on which the spectral analysis is applied in every branch of 

 science has in the last few years brought about important 

 changes in the construction of the apparatus. The greater 

 part of these changes have been prompted, not by theoreti- 

 cal investigations, but by experimental methods, whereby it 

 has happened that many errors have been suffered to re- 

 main in the construction of the apparatus which may have a 

 material and deleterious influence upon the sharpness of the 

 spectrum. Dr. Block has therefore made careful investiga- 

 tion and comparison of such instruments as are now in use, 

 and has developed the theory of the refraction of light in 

 systems of j^risms. He has extended his investigations to 

 converging and diverging bundles of rays, as also to the in- 

 fluence which imperfect prisms, or the inclinations of the 

 prisms can have upon the j^urity of the spectrum. Among 



