VI. 



To Directors of Meteorological Observatories and other Institutions, the 

 beginning of this Catalogue presents a practical selection of Standard Instru- 

 ments, and in many, I believe, will be found a degree of excellence that is 

 unequalled ; in proof of this, I may state that the Standard Thermometers 

 for most of the important investigations at the Kew Observatory, as well as 

 those of the equally comprehensive researches of the most eminent Professors 

 of Cambridge, Oxford, London, etc., have been made at my establishment. I 

 may also mention the arrangements which I designed to meet the require- 

 ments of various Scientific Expeditions and Geographers of our own and other 

 countries, including Livingstone, Burton, Speke, Grant, Hooker, Baker, etc., 

 whilst the whole series of Portable Meteorological Instruments for Travellers, 

 as now used, were expressly designed by me to meet the desires of the 

 Alpine Club. 



To amateurs and others, desirous of taking plain trustworthy meteorological 

 observations, other instruments are described of a simpler kind, at a moderate 

 cost, the indications of which will bear the strictest examination. 



The numerous changes and additions to the Microscope, and at reduced 

 cost, have also received my best care, as shown by the illustrations and 

 descriptions ; whilst Teles.copes and Field Glasses have been so improved 

 and simplified, as to enable me with much pleasure to refer to their respective 

 lists in the Catalogue. 



I have also great pleasure in referring to the improvements which I have 

 made in Aneroid Barometers, whether for indicating changes of the weather, 

 or for measuring great heights or low elevations, which they now do with a 

 degree of precision hitherto unlooked for in' these instruments, as described on 

 pages 33, 34, and 35. 



Though many instruments are enumerated in Optics, Mechanics, Surveying, 

 etc., in which great changes are often being made, my attention is constantly 

 given to such as are really practical and useful, whilst an extended intercourse 

 with the leading authorities and scientific bodies enables me to introduce 

 every novelty of interest as soon as it appears. 



