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were made every two hours, day and night. In 1848 photo- 
graphic registration was introduced, and from then till now 
there has been an unceasing record of the movements of the 
declination, horizontal force, and vertical force magnetometers, 
as well as of the barometer and the dry and wet bulb thermo- 
meters. The anemometers, for direction, force and velocity of 
the wind, and also a pluviometer, register themselves mechani- 
cally. The magnetic observations and registers to 1863 have 
been discussed, and the epitomised results form the subjects of 
various memoirs in recent volumes of the Philosophical Tran- 
sactions. It may be mentioned that among other points these 
discussions negative the existence of a decennial magnetic 
period related to the period of solar spot activity. A great 
discussion of temperature records from 1848 to 1868 is now in 
progress. Within the past few years an important, and we be- 
lieve unique, addition has been made to the photographic 
recording department. The spontaneous galvanic “ earth- 
currents ” that at times become so intense as to interfere with 
telegraphic operations, have been made to record themselves 
perpetually by reflecting galvanometers connected with special 
wires running in N.-S. and E.-W. directions through the Ob- 
servatory, and attached to earth-plates at their extremities. 
A discussion of some of the registers has shown that these cur- 
rents are related to the earth’s magnetism in its disturbed state 
— as during auroral displays — but apparently not in its tranquil 
state. 
In conclusion, it should be stated that the Greenwich ob- 
servations of all kinds are published in yearly 4to. volumes of 
nearly 1,000 pages each, in which every observation is set down 
in the utmost detail, with every instrumental reading as it is re- 
corded by the observer, and (especially in the case of the astro- 
nomical observations) with every step in the reductions exhibited, 
down to the final results, which are given in such a form as to 
be directly available to the theoretical investigator. 
