July, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



163 



Still more striking- are additions made to letters as 

 in Fig-. 2, where the numeral I in II has heen changed 

 mto 7 by the addition of a stroke at the top. 



A fraudulent addition or interlineation may touch the 

 top of another letter and thus give evidence against 

 itself. In Fig-. 3 it will be seen that the words " in full 



.111 i !-<-( ^ ti'rinPP' 





to date" have been manifestly added after the signa- 

 ture of the receipt, as shown by the cros.sing of the "t" 

 in "date" running over and into the top of the initial 

 letter of the signature. In this case the whole question 

 was whether the receipt was given for a definite amount 

 or " in full to date." 



Forged signatures are frequently first carefully out- 

 lined in pencil before being inked in. In such cases the 

 pencil marks can be shown under the microscope not 

 properly covered, and with the graphite caught in the 

 ink film. Any further attempt tO' erase the pencil marks 

 would probably have more or less altered the superficial 

 appearance of the paper. Forged signatures carefully 

 and laboriously drawn from a model with frequent lift- 

 ing's or slopping-s of the pen show the over-lapping of 

 lines and uneven distribution of the ink with astonishing 

 clearness. The tint also of the ink may show on com- 

 parison that a document purporting to be several years 

 old is really only as many days old. Even in type- 

 writing:, comparisons by means of the microscope may 

 show numerous discrepancies and differences. 



r-crforations are often used to prevent fraud, Inil 

 these have been known to be laboriously filled in and 

 new ones made. ITie microscope, however, readily 

 exposes such a fraud, as is shown in Fig. 4. 



Mr. Osborn calls attention to the fact that high 

 powers are not necessary to detect the majority of such 

 cases of alteration of documents. .'\ f; in. is about as 

 high a power as is needed, but there must be good subr 

 stage illumination bv means of a condenser, and means 

 of illuminating opaque objects by a bull's-eye or other 

 wise. Polarizing prisms may be useful in certain cases 

 1)1 paper fibre examination, and micrometer apparatus 

 is essential, as well as drawing apparatus. Photo-micro- 

 graphy is of most valuable service in making exact re- 

 productions. 



The microscope should have a large stage, and for 

 examining: some kinds of disputed documents the micro- 

 scope tube may be mounted with advantage on a special 

 stand witliout a stage, so as to give a largfe open field 

 directly under the objective. In this way it is easy to 

 examine the middle or any other part of a large docu- 

 iiienl. The examination of crossed lines, traces of 

 pencil marks, edges of lines, paper fibres, etc.; the inves- 

 tigation of evidences of re-touching, and the examina- 

 tion of ink conditions may require a higrh power objec- 

 ti\e, but lor examining" writing as such a mag-nification 

 nl Irom ten to fifty diameters is ample. Photo-micro- 

 graphs arc freqLiently useful, and may, in certain cases, 

 be c<niclusi\e c\ idence. The general magnification of 

 such photo-microg;raphs is from twenty to fifty diame- 

 ters, l>ut the objective must be flat in the field and a long 

 camera length is preferable to eye-piecing. A camera 

 lucida attachment for drawing directly from the image 

 in the microscope is useful for making illustrations and 

 outlines, and in measuring. 



Objectives witK Sa.fety Springs. 



Beginneis and elementary students find the very 

 short working distance ol high power objectives 

 a source of dang-er either to the front lens of the 

 objective Or to the cover-glass of the slide, and even 

 more experienced workers are sometimes liable to mis- 

 fortunes of this nature. To- obviate this C. Reichert has 

 fitted Bourgnet's Spring Safety Action to all his high 

 power objectives from J in. upwards. The optical part 

 of the objective is mounted in such a way as to slide 

 bodily within an outer projecting case, the front lens 

 projecting throug-h a circular aperture in the front of 

 this case and kept in position by a spiral spring- above, 

 which rests against a collar inside. Under ordinary cir- 

 cumstances the elasticity of this spring keeps the objec- 

 tive in proper adjustment, but in case of contact between 

 lens and cover-glass the optical part is pushed into its 

 sheath. 



Hanging Drop Prepa.rations. 



Mr. j. K. Collins gives in the British Medical Journal 

 a very simple method of making- a hanging;-drop pre- 

 paration which obviates the usual method of building 

 up a moist cell with rings of wet blotting--paper. A 

 small rubber elastic band of suitable size and thickness 

 is smeared with vaseline on one side, and this side is 

 then placed on the .slide. The upper side of the rubber 

 band is now likewise smeared with vaseline and the 

 cover-glass with its hanging-drop applied to it. An air- 

 tisrhtcell is thus easilv made. 



[Communications and enquiries on Mieroseopieal matters are invited 

 and should be addressed to F. ShiUington Scahs. "Jersey," 

 St. Barnabas Road, Cambridge.] 



