12 NEGEETTI AND ZAMBRA, HOLBORN VIADUCT, E.G., 



18. FitzRoy's Marine Gun Barometer, constructed by Messrs. 

 Negretti & Zambra under the immediate superintendence, and named by permission 

 of, the Admiral for the special use of Her Majesty's navy, mounted with 

 vulcanised India-rubber packing to prevent concussion and breakage caused 

 by gun-firing. 



Packed in case 5 10 



Extra tube for ditto 1150 



See also Section Marine Barometers. 



Trials of the FitzRoy Marine Barometer under Fire of Guns. Some of the first baro- 

 meters made by Messrs. Negretti and Zanibra on Admiral FitzRoy's principle were severely tried under the 

 heaviest naval gun firing, on board H. M.S. Excellent', and under all the circumstances they withstood the 

 concussion. The purpose of the trials was " to ascertain whether the vulcanised India-rubber packing round 

 the glass tube of a new marine "barometer did check the vibration caused by firing, and whether guns 

 might be fired close to these instruments without causing injury to them." In the first and second series 

 of experiments, a marine barometer on Admiral FitzRoy's plan was tried against a marine barometer 

 on the Kew principle, both instruments being new, ani treated in all respects similarly. They were 

 " hung over the gun, under the gun, and by the side of the gun, the latter both inside and outside a 

 bulkhead ; in fact, in all ways that they would be tried in action with the bulkheads cleared away." The 

 result was that the Kew barometer was broken and rendered useless, while the new pattern barometer 

 was not injured in the least. In a third series of experiments, Mr. Negretti being present, five of the 

 new pattern barometers were subjected to the concussion produced by firing a 63-pounder gun with shot, 

 and IGlbs. charge of powder. They were suspended from a beam immediately under the gun, then from a 

 beam immediately over the gun, and finally they were suspended by the arm to the bulkhead, at the 

 distance of only 3ft. 6in from the axis of the gun ; and the result was, according to the official report, 

 "that all these barometers, however suspended, would stand, without the slightest injury, the most 

 severe concussion that they would ever be likely to experience in any sea-going man-of-war." These trials 

 were conducted under the superintendence of Captain Hewlett, C.B., and the guns were fired in the 

 course of his usual instructions. His reports to Admiral FitzRoy, giving all the particulars of the trials* 

 are published in the " Ninth number of Meteorological Papers," issued by the Board of Trade.* 



* With reference to these barometers, we have received the subjoined testimonial, with permission to 

 use as we please. 



" Meteorologic Office, June 12th, 1863. 

 " MESSRS. NEGRETTI AND ZAMBRA, 



" The barometers which you have lately supplied to Her Majesty's ships through this Office are 

 much approved, being good for general service, afloat or on land. 



"(Signed) R. FITZROY." 



Admiral FitzRoy writes : 



" This marine barometer, for Her Majesty's service, is adapted to general purposes. 



" It differs from barometers hitherto made in points of details, rather than principle : 

 1. The glass tube is packed with vulcanised India-rubber, which checks vibration from con- 

 cussion, but does not hold it rigidly, or prevent expansion. 2. It does not oscillate (or 

 pump), though extremely sensitive. 3. The scale is porcelain, very legible, and not liable 

 to change. 4. There is no iron anywhere (to rust*). 5. Every part can be unscrewed, 

 examined, or cleaned, by any careful person. 



" These barometers are graduated to hundredths, and they will be found accurate to that 

 degree, namely, the second decimal of an inch." 



19. Negretti & Zambra's Short Tube Barometer, specially constructed 

 by N". & Z. for Balloon experiments, Altitude Measurements, or for use at 

 elevated mountain stations. p r i ce 770 



