SCIENCE-GOSSIP. 



£ 



1 



The Harvest Bug. — Referring to the intoler- 

 able discomfort caused by the harvest bug. the 

 '" Comptes Rendus " tells us that the identity of 

 the acaroid mite which gives rise to the " bumps " 

 by burying itself in the skin, has been satisfactorily 

 determined. M. Brucker has examined specimens 

 taken from human beings during the iast autumn, 

 and has defined them as the hexapod larvae of 

 TrombiJium gymnopteron. The same animal in the 

 larval form has been found by the author on a rat 

 and on a blackbird, as well as on many plants, 

 especially on kidney beans. As other Trombidian 

 larvae may, in different localities, attack man, it is 

 well to note that those reported on were obtained 

 from Semur-en-Auxois (Cote d'Or), where this 

 autumn plague is specially troublesome. 



Micrometer Measuring Apparatus. — Those 

 of our readers who have experienced a difficulty 

 in accurately estimating the size of minute objects 

 with the ordinary micrometer will be interested 

 in the accom- 

 panying sketch 

 of an apparatus 

 that has been 

 designed bv Mr. 

 J. S. Curtis, of 

 the United 

 States Geologi- 

 cal Survey, and 

 which is used 

 by him, with 

 the aid of the 

 microscope, for 

 the quantitative 

 determination 

 of silver. The 

 measuring ap- 

 paratus is very- 

 simple in con- 

 struction, and 

 may be used 

 with any micro- 

 scope that is fit- 

 ted with crossed 

 bairs in tube or 

 eyepiece It 

 consists of two 

 metallic plates, 

 one above the 

 other, to which 

 a motion paral- 

 lel to one cross 

 hair can be 

 given as well as 



it These two plates are fastened upon a 

 third plate, which is attached to the shelf of the 



cope. The accompanying diagram shows 

 the arrangement and mode of movement of these 



ilcs. The letter a designates the plate upon 

 which the object is placed. This plate has a m 

 parallel to the vertical cross hair given to it by 

 means of the screw i and the ratchet r, ;ind it moves 



plates 1 1 'I hi-, plate <'. thi 



pieces b b, the xcrcw i and the ratchet r all res) 



upon a sccor.'! plate //, which m ec the 



tide piece* c:. across the vertical hair line The 



tl side to side is given to both the upper 



kle by means ol the micrometer screw I. 



the Inch, and the 



■ 



the micrometer r<|,re.<r.' 

 'I lie Ktf 



i, which are used to fatten the 

 bell of the 



microscope stand. Considerable practice is needed 

 to accustom the eye to the apparatus, but as far as 

 accuracy of measurement is concerned, it leaves 

 little to be desired. 



Phosphorescence of Wood. — The phosphores- 

 cence of decaying wood proves to be due to 

 minute vegetation, instead of to purely chemical 

 causes, as some have supposed. The mycelium of 

 some undetermined fungus from pine has been 

 cultivated by Kutscher, a German biologist, in 

 decoctions of beech bark and agar-agar, the result 

 being a white, brilliantly luminous growth. 



Size of Bacteria. — At a lecture on Bacteriology- 

 given by Mr. L. Atkinson before the Pharmaceutical 

 Society, it was stated, with the object of affording 

 some relative idea of the extreme minuteness of 

 bacteria, that the tongue of a fly when flattened 

 out is one-sixth of an inch long. Seen on a six- 

 foot screen the measurement will 

 inches, an enlargement of 450 



C 



J 



=JZ 



ii 



T! 



D 



nv 



■ Measuring Aitakatus. 



be seventy-five 

 diameters, or, 

 estimated super- 

 ficially, 250,000 

 times larger. 

 This amplifica- 

 tion will not, 

 however, enable 

 us to see a trace 

 of most bacteria, 

 many of them 

 only measuring 

 from nTrJ-jjifth to 



3irW a ° f an 

 inch. The power 

 necessary to en- 

 large them to the 

 size of ordinary 

 printers' type 

 would, in the 

 same ratio, en- 

 large the fly's 

 tongue to nearly 

 600 feet, or one 

 and a-half times 

 the height of St. 

 Paul's Cathe- 

 dral. 



Formation of 

 Gold Nuggets. 

 — The theory 

 that gold nug- 

 gets have been 

 deposited from a 

 solution around 

 a nucleus has 

 been a subject of microscopic investigation by 

 Professor A. Liversidge, the Australian mine- 

 ralogist, lie finds that etched sections of nuggets 

 show more or less crystallization, often large and 

 well-defined crystals, sometimes with inclusions of 

 quartz and other impurities, but never concentric 

 layers. Gold that had been fused had a similar 

 crystalline structure. He does not think this neces- 

 sarily proves that native gold has been in a melted 

 in. lint believes that it has been deposited 

 from solution, ami usually in veins and cavities, 

 although possibly around a nucleus. 



11 bra.- Soldanl has shown thai one and 



a hall ounces of limestone from ' ascina, in 



1 , , ■ ontained '",1 , 1 fos .ii foi ms ol foramens, 



and many of them were 01 uti thai ioo weighed 



only a gram An ounce oi and from thi Vntilli 

 was shown by D'Orblgny to contain j,s.to,oou 

 ■pecimi 



