Sherlock Holmes is always depicted with a magnifying glass in his hand but in fact he rarely used it. It was first used during the Enoch J. Drebber case (A Study in Scarlet). Soon after Lestrade discovers the word 'Rache' on the wall of 3 Lauriston Gardens, Holmes gets out his magnifying glass to inspect the room. Also see Double Lens, Lens

 

The first of Sherlock's monographs to be mentioned was that written on the subject of tobacco ash. (A Study in Scarlet). In The Sign of Four he explains that 'Upon the Distinction between the Ashes of the Various Tobaccos' is about 140 forms of ash with coloured plates.

In another, upon the tracing of footsteps, he explains the uses of Plaster of Paris in preserving the impressions of shoes. (The Sign of Four)

In a third, upon the influence of a trade upon the form of the hand, has lithotypes of the hands of slaters, sailors, cork-cutters, compositors, weavers and diamond-polishers. (The Sign of Four)

 

 

This is where Holmes kept his hypodermic syringe. (The Sign of Four)