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OBITUAEY. 



Henri van Heurck. 

 By J. B. De Toni, Hon.F.E.M.S.* 



To the gaps already made in the ranks of the Honorary Fellows 

 of the Society through the death of F. Castracane and J. Brun is 

 now added another no less lamentable. Henri Ferdinand van 

 Heurck, Professor of Botany and Director of the Botanic Garden 

 at Antwerp, died in that city on March 13th, 1909. 



H. van Heurck was born at Antwerp on August 28th, 1838. 

 He began his scientific career by writing papers on floristic and 

 medical subjects, but he soon became attracted to the study of 

 Microscopy and especially Diatomology, soon taking rank among 

 the most distinguished authors in these branches of science. 



His handbook, Le Microscope, first published in Paris in 1865, 

 has passed through subsequent editions, each an improvement 

 upon its predecessor, in 1868, 1878, and 1891, in addition to the 

 English translation published in London by Mr. Wynne E. Baxter, 

 F.L.S. 



H. van Heurck delighted to occupy himself with discussions 

 relating to the optics of the Microscope, at one time studying the 

 new combinations manufactured by E. Hartnack, Boss and Co., 

 Powell and Lealand, Hasert, Eeichert, and Zeiss ; at another the 

 camera lucida, the camera obscura, the illumination of objects 

 under the Microscope; at another, again, the most appropriate 

 liquids for the immersion and preservation of prepared objects. 

 Of all these papers, suffice it to mention two — (1) his Etude des 

 Objectifs Apochromatiques (1899), in which, after giving an histori- 

 cal and theoretical introduction, he summarises the chief forms of 

 modern apochromatic objectives, and finally tabulates and compares 

 the relative merits of the 3 mm. and 2 mm. apochromatics of the 

 most modern types ; (2) his Les Mediums a haute indice, in which 

 he gives an excellent account of the resinous and chemical media 

 employed for mounting diatoms — viz. Canada balsam, styrax, 

 liquidambar, napthalin monobromide, methyl iodide, and Smith's 

 arsenical medium (realgar dissolved in bromide of arsenic). 



Henri van Heurck, having acquired a profound knowledge of 

 the theory and practical use of the Microscope, dedicated himself 

 almost exclusively to the study of the Diatomacere, discussing in 

 his papers the structure of the valves, and above all the nature of 



* Translated and edited by A. Gepp, M.A., F.L.S. 



