867 



even in the physical sciences most dependent oh applied mathema- 

 tics, sooner or later a stage is arrived at whea for further progress 

 instruments are of vital importance. 



Without instruments even the theory of gravitation would have 

 been little more than a sublime speculation ; and the theory of light 

 at the present moment is perhaps in that condition when that ma- 

 thematician would effect the most who best prepared the way for 

 judicious and refined experiments. Such being the importance of 

 instruments, this Society I am sure cannot have failed to take a lively 

 interest in the improvements in progress at Greenwich. In 1843, 

 the Astronomer Royal proposed that an altitude and azimuth instru- 

 ment should be constructed with a peculiar adaptation of materials, 

 so as to secure as far as possible exemption from change, and so make 

 it practicable to observe with great accuracy at a distance from the 

 meridian. The object was a very important one ; to procure a more 

 extensive, and a more complete series of lunar observations ; and 

 when we recollect that Greenwich has had the honour of supplying 

 the world with the best series of lunar observations extant, that upon 

 that series the lunar theory and the lunar tables rest, surely it was 

 an object, if not of national pride, at least of great scientific interest, 

 that in that department of astronomy at least nothing should be 

 wanting which could add to the efficiency of the National Observa- 

 tory. The instrument was soon after commenced, designed by the 

 Astronomer Royal ; it has now been for some time in use, and I 

 believe fully answers the purpose. 



It had been found that the meridian instruments were of insufficient 

 optical power for observing the minute planets, and the faint stars 

 used as stars of comparison. In consequence, the Astronomer Royal 

 designed a transit circle to carry an object-glass of eight inches 

 aperture, and twelve- and- a-half feet focus ; to be made of cast iron, 

 with the same precautions against change which had been found so 

 effectual in the altitude and azimuth instrument. Cast iron, being 

 stiffer than brass and expanding less with heat, possesses great ad- 

 vantages ; and unless it shall be found to be more liable to permanent 

 change of figure under moderate strain, it will probably hereafter 

 enter very largely into the construction of astronomical instruments. 

 The great transit circle is in progress, and when completed no doubt 

 it will be worthy of the place it is destined to hold among the 

 Greenwich instruments. 



Important however as these new instruments will be as a means 

 of making better and more numerous observations at Greenwich, I 

 think they are still more important to science, as unquestionable in- 

 dications of progress in the construction of astronomical instruments 

 in this country. Traditional routine seems here for many years to 

 have kept us behind our continental rivals in this noblest department 

 of mechanical art. Astronomers above all other persons are ajDt to 

 cling with pertinacity to the imagined perfection of their instruments 

 and methods ; and the artists who construct the instruments, con- 

 scious of their own practical skill, and not unfrequently deficient in 

 the high theoretical knowledge required to guide it, are still more 



