xxxii GENERAL SUMMARY OF SCIENTIFIC AND 



The Centennial Exposition at Pliiladelphia has also been of con- 

 siderable importance to American meteorologists. There was ex- 

 hibited there, in active operation, the very beautiful and efficient 

 printing meteorograph, invented by Theorell, of Sweden, as also one 

 by Baumhauer, of Haarlem. 



Apparatus by the best European and American makers was also 

 exhibited ; especially noticeable was tiie complete display by the 

 Army Signal Office of its own methods and instruments. 



The general rules for observers as recommended by the Vienna 

 Congress of 1873 have been very widely accepted by national sys- 

 tems of meteorological observation, as shown by the annual reports 

 of Wild at St. Petersburg and Scott at London ; and especially in 

 the uniformity introduced into the j^ublications of the climatological 

 observations at Vienna, Christiania, Co23enhagen, London, St. Peters- 

 burg, and Constantinoi^le. 



The aneroid barometer has received great attention of late years, 

 and bids fair to rival the ordinary mercurial barometer for most pur- 

 poses. The best instruments appear to be those made by Naudet 

 & Co., of Paris, and Goldschmid, of Zurich, both of which embody 

 improvements that ai3pear not yet to have been adopted by other 

 makers. 



Tlie ordinary aneroids have been made the subject of a rather 

 careful investigation by Grassi, of Pavia, who has considered espe- 

 cially their adaptation to hypsometric work. In the course of his 

 memoir he brings to light the liypsometric formula of St. Robert, 

 Avhich seems to be but little known outside of Italy, but which gives 

 quite as good results as Ruhlmann's. 



Professor Schreiber, of Leipsic, has also paid much attention to 

 the reliability of the aneroid barometer, and maintains that with 

 proper care the instruments of Goldschmid, Hipp, and Naudet are 

 probably equal in reliability to mercurial barometers, provided only 

 that a proper degree of care be taken in their use. Both kinds of 

 instruments are, he maintains, essentially relative, rather than abso- 

 lute, in their indications ; both are liable to serious accidental errors 

 and changes, and both require to be transported with the same ten- 

 derness. He especially criticises the too common habit of reading 

 the aneroid as it hangs vertically, and maintains that it should be 

 kept with its face horizontal, quite as carefully as a marine chro- 

 nometer which is hung in its gimbals. 



Staff- Engineer George, of the British Navy, projDoses to refill a 

 mercurial barometer, when used in traveling, at every station occu- 

 pied by the observer, and to empty it before packing it away for 

 transportation. He removes any bubbles of air that might be likely 

 to remain in the tube, not by boiling the mercury, which is both te- 

 dious and dangerous, but by mechanical means, viz., the introduc- 

 tion simply of a wire, to the end of which a feather is attached, the 



