128 Boss's New One-Twelfth. 



to the comparison of these two or three examples, that, in all the 

 engravings of objects found in the lacustrine habitations I 

 have yet seen, the pottery seems to me to be universally of 

 the same character, a matter of very serious consideration for 

 those who shall write in future on these remarkable Swiss re- 

 mains. To the present time, their predecessors have been 

 making appropriations which will not stand for a moment be- 

 fore the careful researches of the judicious antiquary. M. 

 Troyon (Habitations Lacustres, plate vii., fig. 35) ascribes a vase 

 to the " stone age," and (in plate xiii.) gives another to the 

 so-called " age of bronze," both which belong undoubtedly — 

 I might almost say ridiculously so — to the Alemannic or Frank - 

 ish pottery ! It is certainly a circumstance not to be over- 

 looked, that over the whole extent of Switzerland to the forest 

 borders of Italy and Germany, all the pottery found in these 

 lacustrine habitations should belong- to one class, and that be- 

 longing to a period embracing probably the greater part of 

 the fifth and sixth centimes after Christ. 



BOSS'S NEW £th.— THE EEQUISITES FOR 

 HIGH POWERS. 



The letter of Mr. Brooke which we published in our last 

 number will help to stimulate microscopists to pay attention to 

 the qualities they should seek in deep objectives for the micro- 

 scope, and to the reasons for selecting one power in preference 

 to another. We hope Mr. Brooke will continue his inquiries, 

 and, in the meanwhile, we beg to offer the following remarks. 



The question raised by Mr. Brooke's letter is whether a 

 ^th objective, of large angular aperture and exquisite workman- 

 ship, is to be accepted as the glass of the shortest focal length 

 which it is desirable for ordinary purposes to make or employ. 

 The late Mr. Ross, after experimenting on the subject, was of 

 opinion that a ~Xh. objective could be made so as to take in all 

 the light practically obtainable from any object, and that it 

 admitted of more perfect corrections than could be given to 

 combinations of shorter focus. The small diameter of the front 

 lens of high powers precludes their admitting the quantity of 

 very oblique rays usually indicated in describing their angular 

 aperture. The real quantity of such rays is considerably less than 

 that computed according to formula in current use ; but it is 

 easy to understand that the front lens of Mr. Ross's ^th, when 

 brought within about 006" of an object, may take in quite as 

 much, or more, of the oblique rays than could enter a smaller 



