1886.] 



MICROSCOPICAL JOUENAL. 



233 



of useful magnifying power, which 

 is fixed by the limit of aperture at 

 present attainable, can already be 

 reached, without loss, by an objective 

 of the focal length of 3 mm., as the 

 latter objective w^ill bear the applica- 

 tion of correspondingly higher eye- 

 pieces without any appreciable detri- 

 ment to its performance. 



The objectives (homogeneous im- 

 mersion) of 1.30 aperture have so 

 great a woi^king distance that they 

 will work through covers more than 

 0.3 mm. in thickness. With an ap- 

 erture of 1 .40 the working distance 

 is reduced to 0.35 mm. These ob- 

 jectives i"equire very careful handling, 

 because, in order to obtain the larger 

 aperture, the metal setting of the front 

 lens has to be turned extraordinarily 

 thin, so that any blow or strong pres- 

 sure upon the front objective is likely 

 to injure it. For both reasons, there- 

 fore, the objectives with the slightly 

 lower aperture are undoubtedly more 

 convenient for regular use. The 

 larger aperture will, however, of 

 course allow of a rather higher degree 

 of optical performance being reached. 

 No attempt is made to exceed an 

 aperture of i .40, as the small percent- 

 age of possible increase would ren- 

 der the objectives almost valueless 

 for any scientific investigation. 



With regard to the price of ob- 

 jectives which, especially in the case 

 of the dry series, may appear to be 

 very high in comparison with the 

 usual charges, it must be borne in 

 mind that the appochromatics are far 

 more complicated in their construc- 

 tion, and if their special qualities are 

 to be maintained, they must be far 

 more difficult to manufacture than 

 the ordinary objectives. Moreover, 

 the number of such objectives manu- 

 factured must be extremely limited, 

 even with the resources of a large 

 factory. The objectives, however, 

 like all the productions of our firm, 

 stand on an absolutely free basis. 

 The glass employed is, by our instru- 

 mentality, accessible to any one, and 

 no optician is, in the least degree. 



prevented from producing the same 

 objectives as good and as cheap as he 

 can. 



{To he continued. \ 



EDITORIAL. 



Publisher's Notices. — All communications, ex- 

 changes, etc., should be addre'ised to Henry Leslie 

 Osborn, Lafayette, Indiana, Purdue University. 



Subscriptions, and all matters of business, should be 

 addressed to the Eubiness Manager, P. O. Box 630, 

 Washington, D. C. 



The address of Mr. R. Hitchcock is Osaka, Japan. 



Subscription price $1.00 PER YEAR strictly in ad- 

 vance. All subscriptions begin ivilh the January 

 nutnber. 



A pink wrapper indicates that the subscription has 

 expired. 



Remittances should be made by postal notes, money 

 orders, or by money sent in registered letters. Drafts 

 should be made payable in Washington, New York, 

 Boston, or Philadelphia. 



The regular receipt of the Journal, which is issued 

 on the 15th of each month, will be an acknowledgment 

 of payment. 



The first volume, 1880, is entirely out of print. The 

 succeeding volumes will be sent by the publisher for 

 the prices given below, which are net. 



Vol. II (1881) complete, $1.50. 



Vol. Ill, $2 50. 



Vol. IV (1883) complete, $1.50. 



Vol. V (1884) complete, $1.50. 



Vol. V (1884), Nos. 2-12, ^i.oo. 



Vol. VI (1885), $1.50. 



Vol. VII (1886), $1.00. 



To Our Readers. — With this 

 number the Joicrnal closes its sev- 

 enth volume and enters upon a new 

 volume and a new year. As our 

 readers are well aware the former edi- 

 tor, Prof. Romyn Hitchcock, who has 

 managed it from the start and brought 

 it to its present good repute, is now far 

 away in Japan. He watches it still 

 with the deepest interest, but from 

 afar. 



His absence from this country for an 

 indefinite period rendered it necessary 

 that the Journal should pass into the 

 permanent charge of those who would 

 treat it as their own. Early in the 

 present year its business interests 

 were placed in the hands of Mr. 

 Rufus W. Deering, of Washington, 

 D. C, who will still control its en- 

 tire business arrangements and keep 

 the office of publication at Washing- 

 ton. During the past summer we 

 undertook, temporarily, the editorial 

 charge pending the adjustment of cer- 

 tain details, and are now happy to an- 

 nounce that the present arrangement 



