Jason Clarke Antiques has dated this piece to the 1870s.
The upper middle section of the dial has the maker’s name Negretti & Zambra and “Instrument makers to her Majesty” below with the lower middle section stating numerous addresses at “Holborn Viaduct, Cornhill, Regent Street and Fleet Street”. It has a blue steel pointer and a brass set hand operated by a brass knurled dial to the centre.

The piece comes complete with its original hanging loop and adjustments for elevation can be made by means of a screw at the back of the instrument.
A nice clean example of its type and through the use of the addresses on the dial, we can pinpoint the manufacture date quite concisely to between 1869 and 1873 when the company held premises at both Holborn Viaduct and Fleet Street at the same time.

Negretti & Zambra were a leading name in the production of meteorological and scientific instruments and had a company history dating back to 1850 although their parents were amongst those Italian emigres that bolstered the British meteorological instrument making industry at the turn of the century.

Throughout their long and esteemed history they exhibited at British and international industrial fairs and became makers to both Queen Victoria and Edward VII. Owing to changes in the business, the firm ceased the public retailing of scientific instruments sometime around the late 1960’s and continued with a focus on the aviation industry in numerous guises until its eventual liquidation in the year 2000. They are today perhaps the most collected of the scientific instrument firms which bears testament to the quality of their work.
Circa 1870.
Jason Clarke Antiques has dated this piece to the 1870s.
You can view the stock and full dealer information on the Jason Clarke Antiques Profile Page