December 9, 1921] 



SCIENCE 



569 



manufacture oil-immersion objectives of this 

 aperture (0.80 IST. A.). With such an objec- 

 tive the worker eitlier in biology or in medi- 

 cine can get good results even vyithout a 

 very profound knowledge of the optical princi- 

 ples involved. He can also go forward with 

 his work with full confidence that the objec- 

 tive being used will give good results, and 

 every worker knows the importance of confi- 

 dence in his apparatus for successful accom- 

 plishment. Finally, during the past summer 

 and autumn the Bausch and Lomb Optical 

 Company of Rochester, N. T., undertook the 

 manufacture of the desired medium-aper- 

 tured oil-immersion objectives. The outcome 

 is all that could be asked; and they have 

 been subjected to the most rigid tests in 

 actual practise in the fields in which dark- 

 field work is applied. These objectives are 

 now available, and the writer feels confident 

 that every one using them will feel grateful 

 for the freedom from worry that was always 

 involved in modifying a high-apertured ob- 

 jective for the dark field. 



It is only fair to add that no matter how 

 enthusiastic one may be over the possibilities 

 of dark -field microscopy, much more skill is 

 necessary in it than for the ordinary bright- 

 field microscopy. I think that all who have 

 used the dark-field microscope successfully 

 will agree that the ideal plan for an indi- 

 vidual or for a laboratory is to have a micro- 

 scope devoted to this work alone. If then 

 a proper electric light is available, one can 

 proceed to make examination of specimens 

 with the dark-field microscope with the same 

 certainty and rapidity with which examina- 

 tions are made with the bright field. 



It may be stated in passing with reference to 

 these new objectives, that they have certain advan- 

 tages for ordinary bright-field work. As ordinarily 

 employed the oil-immersion objectives of high aper- 

 ture (1.40 to 1.20 N. A.), are used in bright-field 

 work without oil-immersion contact between the 

 under surface of the slide and the top of the bright- 

 field condenser. As light of an aperture greater 

 than 1.00 N. A. can not emerge from the condenser 

 into air, it follows that not nearly all of the avail- 

 able aperture is employed. It was believed there- 



fore that these medium-apertnred objectives would 

 serve to give practically as good images for his- 

 tological, embryological and pathological specimens 

 as the high-apertured objectives as ordinarily used. 

 Actual tests proved the correctness of this suppo- 

 sition. Of course when the resolution of fine details 

 is involved the higher aperture is of great import- 

 ance, but in order to be fuDy utilized the micro- 

 scopic slide must be in immersion contact with the 

 top of the condenser. 



Simon H. Gage 

 Cornell University, 

 Ithaca, N. Y. 



THE INTERNATIONAL GEOLOGICAL 

 CONGRESS COMMITTEE 



At the twelfth session of the International 

 Geological Congress, the president was in- 

 structed to nominate a committee to consider 

 the question of a permanent constitution and 

 to submit a proposal thereon to the next ses- 

 sion of the Congress. The following com- 

 mittee was appointed: R. W. Brock, Presi- 

 dent; J. S. Anderson, C. Barrels, A. Karpin- 

 sky, A. Renier, Geo. Otis Smith, G. Stein- 

 mann and E. Teitze. 



The committee met in the rooms of the 

 Geological Society of London on July 20, 

 1921. There were present: R. W. Brock, 

 President; A. Renier, Geo. Otis Smith and 

 F. D. Adams (ex-officio member). 



At a preliminary conference called to ob- 

 tain for the guidance of the committee the 

 opinion and advice of a wider and more 

 representative body, the following resolution 

 had been passed: 



That this meeting is of opinion that the question 

 of the establishment of an International Geolog- 

 ical Union should be considered at the next Inter- 

 national Geological Congress, and that it is unde- 

 sirable that any steps should be taken until the 

 question has been so considered at a full and rep- 

 resentative gathering of geologists. 



A concise proposal with regard to a consti- 

 tution to submit for the consideration of the 

 next; International Geological Congress was 

 drawn up, the main points of which are as 

 follows : 



The purpose of the International Geological Con- 

 gress, it was stated, is to advance scientific investi- 

 gations relating to the earth from the point of view 



