156 SUMMARY OF CURRENT RESEARCHES RELATING TO 



errors were calculated by the method of least squares. The following 

 were the results : — 



Estimation error, -015 to -059 mm.; 



Coincidence error, -002 to -014 mm. ; 



Adjustment error, • 0018 to • 034 mm. 



The author concludes from his experiments that from an interval of a 

 certain magnitude the relative error of estimation (that is the ratio of the 

 error to the interval) increases as the latter diminishes ; this increase of 

 relative error is, however, not rapid enough to involve an increase in the 

 absolute error of the measurement, so that using the naked eye it is 

 possible to measure more accurately with fine than with coarse gradua- 

 tions. 



Carlisle Microscopical Society and Dr. Dallinger. — Dr. Dallinger, 

 P.R.M.S., in accepting an invitation to be an Honorary Vice-President of 

 the Carlisle Microscopical Society in place of the late Dr. Carpenter, wrote 

 to Mr. C. S. Hall, the President of the Society, — 



'' I have delayed writing in detail up to this time, in the earnest hope 

 that I might find time to say something to the Society in my letter that would 

 give direction, or stimulus, to the work it so wisely undertakes. But the 

 pressure upon me by the claims of work, compulsory or self-imposed, is so 

 great, that 1 fear if I delay until I can do, in relation to my words of 

 direction or help, as I would, I shall do nothing. I therefore write the 

 rather to express my deep anxiety that the members of your Society should 

 first of all keep, individually and collectively, before them the fact, that the 

 raison d'etre of the modern Microscope is its scientific employment. This 

 can only be the result of a complete mastery of the instrument in all its 

 details. The capacity to bring out what the highest optical skill has put 

 into a lens, is one that in this day, when objectives of the first quality are 

 of such a high order of merit, cannot be overestimated. We may determine 

 on a certain line of delicate investigation, say the working out in persistent 

 continuity of the life-history of some typical form of a group of Infusorians 

 of a relatively large size (and splendid work is waiting to be done in this 

 direction), yet, unless the worker is master of bis lenses — able, that is to say, 

 to make them obey him without difficulty, yielding precisely the results he 

 wants, and not wanting anything from them that they cannot yield ; making 

 the utmost and best use of aperture, collar, and fine-adjustment; and 

 knowing accurately what eye-piecing any given lens will admit of. These 

 and many other things are of the utmost importance. But they imply 

 steady effort and practice : these, with a fair knowledge of the construction 

 of the instrument, are the keys to success, and they can be acquired by any 

 resolute man. But beyond this the management of light and illuminating 

 apparatus is of the first importance. If anything, this is more difficult to 

 fully master than the efficient employment of the lens ; for the use of the 

 lens to its utmost capacity depends upon it. But it is equally within the 

 reach of the resolute. It is when a man is master of his Microscope, as the 

 skilful organist is of his organ, that he will enter without hesitancy, and with 

 certainty of result, upon such investigations as, in every department of 

 biology, and indeed of science, invite the interest and effort of the 

 microscopist. 



Of course, what I have said applies in increasing ratio to the higher 

 power lenses. But it has also a meaning when applied to any power. 

 Relatively very few amateurs have discovered the outside power of their 

 lenses. I can see that by the use of the new achromatic lenses, the difficulty 

 of the use of high powers of great aperture will be lessened ; but perfect 



