272 M. C. COOKE ON BLACK MOULDS. 



systems of classification are all modified and changed, if not passed 

 away. Although claiming no special superiority for the method so 

 extensively adopted by myself, I will briefly describe it. All draw- 

 ings are made to an uniform scale, by means of a Nachet camera. 

 This peculiar form has the advantage of being used with the micro- 

 scope oblique. It is permanently attached to the eyepiece, and when 

 any object is presented on the field which it is considered advisable 

 to draw, it needs only to turn down the camera and draw it without 

 moving object, microscope, or light, in the slightest. A tripod col- 

 lector's microscope always stands at the same angle, and the image 

 drawn on the table beneath is always precisely of the same scale, so 

 that this scale once accurately determined is always the same. All 

 measurements can be made from the drawings, with the previously 

 constructed scale, and this uniformity is practically so useful that the 

 eye becomes accustomed to appreciate the dimensions, and can esti- 

 mate within -g-o^o-th of a millemetre, without using the scale. As 

 this method has been adopted by several microscopists, from my 

 example, with satisfaction to themselves, I may fairly assume that it 

 is one which, for simplicity and practical utility, commends itself to 

 the notice of members of the Club. As a matter of detail, it may 

 be mentioned that copies of the Nachet camera have been manufac- 

 tured by Mr. Swift. 



And now, gentlemen, permit me to thank you for the patience with 

 which you have listened to the details of a subject foreign to your own 

 pursuits, and to express a hope that the illustrations and the argu- 

 ments adduced from them may attain their desired effect. That some 

 one or two may be led to see the error of their ways, and be con- 

 verted to this doctrine of the Conservatism of Force. That, setting 

 before themselves a definite and decided career, which shall be alike 

 honourable to themselves, useful to others, and of advantage to 

 Science, they may, by persevering endeavour, become Master in some 

 one of the workshops of Science, and not as heretofore only illus- 

 trations of the homely proverb, " Jack of all trades, and master 

 of none." 



DESCRIPTION OF PLATES XXIV. TO XXVII. 



Fig. 



1. Monotospora sphserocephala, B. ^ Br., from Britain. 



2. Helinintkosporiimi stemphylioides, Corda, from Edinburgh. 



3. ,, rhopaloideB, Fres., from Forden. 



4. „ fusiforme, Corda, from Forden. 



