76 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



with reference to its efficiency. These notes are reprinted 

 from advanced sheets of the journal of the Franklin Institute, 

 to which the article was originally communicated. 12 A, 

 November 30,1871,85. 



NOMENCLATURE OF OBJECTIVES. 



Dr. Woodward, of the Army Medical Museum, in speaking 

 of the nomenclature of achromatic objectives, and of the com- 

 pound microscope, takes exception to the method of estima- 

 ting their power by their real or supposed agreement, in the 

 amount of magnifying, with single lenses of specified focal 

 lengths. Thus, when we read of inch, half inch, and quarter 

 inch objectives, we are expected to understand combinations 

 agreeing in magnifying power with single convex lenses of 

 the focal length named. After a critical discussion of the 

 formula for expressing the relationship between the distances 

 of the object and the lenses to each other, and their magnify - 

 power, the doctor finds that in compound lenses, instead of 

 having one value for all distances, as with the single lens, we 

 may have as many different values for the principal focus as 

 there are distances used. After a full consideration of all the 

 circumstances, he concludes that the best interest of makers 

 and purchasers of instruments would be consulted if the pres- 

 ent nomenclature were abandoned altogether, and objectives 

 named instead by their precise magnifying power without 

 eye-pieces at some selected distance, this to be always ex- 

 plicitly stated. 4 Z>, June, 1872, 40G. 



THE REFRACTION OF LIGHT. 



An elaborate series of observations has recently been made 

 at the Royal Observatory,, Greenwich, to settle the disputed 

 question in optics whether the thickness of the object-glass 

 has any influence on the position of a star seen through it, in 

 consequence of a change in the aberration of the light. It is 

 well known that the refraction which a ray of light undergoes 

 on entering a medium depends on the angle of incidence, so 

 that if it strike the refracting surface perpendicularly, it will 

 suffer no refraction at all. It is also known that the stars ap- 

 pear displaced from their true position about twenty seconds 

 whenever the earth in its motion round the sun moves in a 

 direction nearly at right angles to that of the star. The true 



