226 BemarJiS on a " Note on Ami:)hipleura pellucida," &c. 



corresponded with the " actual power " when the magnifying power 

 was measured by any proper method. 



In the majority of cases I have found the " error " to be in 

 favour of the objective ; that is, the " nominal power " was less 

 than the actual power, and the objective consequently " underrated " 

 in power, sometimes to quite a large amount. 



Dr. Woodward in his note is very careful to give the proper 

 rating of the Tolles' objective, after giving its magnifying power 

 at 48 inches distance between the micrometer and screen ; he says, 

 " It is therefore of rather higher power than a ith, but less than 

 a ith," which is undoubtedly correct. 



A little farther on in his note Dr. Woodward gives the power 

 of another objective by means of figures ; I allude to the so-called 

 immersion yVth of Powell and Lealand. Applying Dr. Woodward's 

 rule to his figures giving the " actual power " of the so-called -iVth, 

 would make it " therefore of rather higher power than a -ioth, hut 

 less than a ^th ; at any rate Dr. Woodward's figures make Powell 

 and Lealand's objective just four times the power of Tolles' ; and 

 according to my way of figuring, the above would be correct, that 

 is, the Powell and Lealand objective would be between a gVth and 

 a ^th, depending upon the position of the " cover adjustment." 



I call it nothing more nor less than deception in Powell and 

 Lealand (or any other maker) in marking an objective nearly 33 per 

 cent, less than its actual power, thus misleading people who cannot 

 make actual comparisons ; and I consider Dr. Woodward guilty of 

 an equal amount of deception in hnoivingly putting forth work done 

 by that objective as having been done by a xVth. 



Dr. Woodward says " that the new ith cannot be claimed to 

 supersede the higheet powers at present in use " (meaning the so- 

 called iVth, the sVth, and the ^'oth of Powell and Lealand, I 

 suppose), " yet nevertheless is not, in my opinion, injurious to the 

 3^th." Such innocence is refreshing j the fact of the J th not " super- 

 seding" objectives of from four to ten times its power not being 

 " injurious " to it is decidedly rich. 



No one, so far as I know, has claimed that Mr. Tolles' iths 

 were to "supersede the highest powers now in use"; but if Mr. 

 Tolles, Powell and Lealand, or any other maker should make a ^^th 

 that would do better than the best yVths or rVths of the present 

 day, it would be " glory enough." 



