36 [March 20, 



intelligent observers of the moon accustomed to extra-meridional ob- 

 servations. 



16. The first desideratum then is an Equatorial Instrument, con- 

 structed with the conditions of ample optical power, great steadiness, 

 delicate adjustment, including a sufficient range for latitude, the 

 usual circular and micrometrical readings, clock-movement, &c., 

 so that it may be in every point of view adapted for special obser- 

 vations of the moon (sun, planets, comets, &c. may also be observed), 

 and be available for many years, in the same optical and space-mea- 

 suring condition. According to my view, founded on experience 

 with various instruments, it must be an achromatic, mounted on a 

 transportable solid stand, placed under the roof of a removeable ob- 

 servatory, capable of holding a clock and, if need be, a small transit. 

 The object-glass should be of 6 inches diameter, the focal length 1 6 

 or 1 7 diameters. 



Such an instrument has actually been made by my direction ; it is 

 finished, and stands complete in the workshop of the skilful artist, 

 whose name is a guarantee of excellence, Mr. T. Cooke of York. 

 Thus the first requisite to give effect to my proposal is practically 

 reached. 



1 7. The second desideratum is that the instrument shall become 

 the property of some scientific body constituted for long endurance, 

 and endowed with so much influence as to be able to give effect and 

 gain adherence to a plan of continuous work, by definite persons, 

 for such periods of time as each in succession may command. The 

 instrument to be confided to each in succession, and mounted in a 

 convenient manner for his use, at his home, during the time 

 appointed. Each observer to furnish, at least once a year, an 

 account of his observations, with drawings on the plan already 

 detailed in the instructions furnished by the Moon Committee of 

 the British Association. At the conclusion of his appointed period 

 of observation, the instrument to be again at the disposal of the 

 scientific body to which it belongs, either to be transferred to 

 another observer, or to be again entrusted to the first observer, 

 according as may seem best for the attainment of the object in 

 view. 



18. I entertain no doubt that, after the operation of one or two 

 years, each yielding fruit, there will be no other difficulty of obtaining 



