HARD WICKE' S SCIENCE- G OS SIP. 



163 



The crops of winter beans have this year been a 

 failure in the neighbourhood of Peterborough, and a 

 well-known agriculturist sent Dr. Griffiths a number 

 of the plants for examination. The roots of the 

 beans were covered with "small boils," which 

 appeared to be living on the plant and keeping it 

 down. Dr. Griffiths found that these "boils" were 

 due to the growth of a parasitic fungus, and that 

 both the fungus and its spores were entirely destroyed 

 by iron sulphate. Iron sulphate can be purchased at 

 half-a-crown per hundredweight. 



" My Microscope, and some Objects from my 

 Cabinet ; a simple Introduction to the Study of ' the 

 infinitely little.' By A Quekett Club Man," is an- 

 nounced for immediate publication by Messrs. Roper 

 and Crowley. The little volume is dedicated to the 

 president and members of the Quekett Microscopical 

 Club. 



A new competitor for public favour is announced 

 for September next, "The Naturalists' Monthly," 

 to be edited by Dr. J. W. Williams. 



MICROSCOPY. 



Amphipleura pellucida. — In Science-Gossip 

 for last November (p. 258), a correspondent enquired 

 for the best way of showing the Amphipleura pellucida, 

 sometimes called Acus, from its needle-like form. I 

 believe the most effectual mode is by means of 

 Wenham's Reflex Illuminator, first described in 

 vol. vii. of the "Monthly Microscopic Journal." 

 As whatever Mr. W. states may be thoroughly relied 

 upon, I will give one extract as a sample : " Amphi- 

 pleura pelhccida assumed a substantial appearance, not 

 seen in any other way ; and at once displayed its 

 striae with a gth that had never resolved them before." 

 The essay is illustrated by a diagram drawing (greatly 

 magnified) and showing that the new instrument is 

 capable of producing a far greater amount of oblique 

 reflexion than had ever been previously effected. If 

 your correspondent (W. E. Simmons) has an oppor- 

 tunity of examining the aforesaid journal, the xiv. 

 vol. (1875) contains much more about it. To save 

 him time in hunting, I may add that the description 

 in vol. vii. (1872) is at p. 237, and the further informa- 

 tion (in vol. xiv.) is on pp. 30, 156, 295, 299. — 

 Observer. 



The Royal Microscopical Society. — The 

 June part of the "Journal" of the above Society, 

 besides the usual full and accurate " Summary of 

 Current Researches," contains an illustrated paper by 

 Mr. P. H. Gosse on " Twelve new Species of Roti- 

 fera." 



Enock's Slides.— The last of Mr. Enoch's issues 

 is the head of the devil's coach horse-beetle 



( Ocypus olens) showing, in the clearest manner, all 

 the mouth organs almost as perfectly as in their 

 living state. The sketch accompanying the slide, is 

 of the greatest use to the anatomical entomological 

 student. 



Magnifying Powers. — In reply to F. Worgan, I 

 subjoin Zeiss's magnification of the objectives with the 

 several Huyghenian eye-pieces and with a body 

 length of 155mm. — P. jfamieson. 



Camera Lucida. — In reply to Mr. Brokenshire's 

 first query, the paper should be placed at a distance 

 of ten inches from the eye, the microscope being of 

 course focussed so that the final image appears in the 

 plane of the paper. The linear magnification of 

 the drawing is then equal to the magnifying power 

 of the combination. Any other distance at which 

 objects can be seen distinctly, might have been taken 

 as the standard distance, instead of ten inches, and 

 the measure of the magnifying power would be 

 increased accordingly. But the standard distance 

 being once fixed, all microscopes must be referred to 

 the same standard, and ten inches is almost uni- 

 versally adopted. By placing the paper at a greater 

 distance, the actual magnification of the drawing may 

 be increased in proportion, but the apparent size of 

 the image, measured by the angle which it subtends 

 at the eye, will be practically unaltered by the 

 necessary focussing, and the magnifying power will 

 therefore be the same, and will no longer be equal to 

 the magnification. I hope this is sufficiently clear, 

 for there is rather a tendency to confuse magnification 

 or amplification, which depends on how the micro- 



