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XXVIII. On the Construction of Specula of Six-feet Aperture; and a selection from the 
Observations of Nebulae made with them. By the Earl o/’Eosse, K.B.., Ac., F.B.S. 
Eeceived June 5, — Eead June 20, 1861. 
The period seems now to have arrived when it may he proper to lay before the Eoyal 
Society some further account of researches in sidereal astronomy, carried on with a 
Newtonian telescope of 6-feet clear aperture. 
The observations extend over a period of about seven years, during which few favour- 
able opportunities were lost ; stiU in our chmate, where there is so much cloudy weather, 
a year’s work, measured by the number of hours when nebulae can be effectively observed, 
is not considerable. Here in winter the finest definition we have, and the blackest sky, 
is usually before eleven o’clock, after which the sky becomes luminous, and the fainter 
details of nebulae disappear. In spring and autumn the change is neither so early nor 
so decided; but the nights are shorter. Guided by Sir John Hekschel’s admirable 
Catalogue, we have examined almost all the brighter kno-wn nebulae except a few in 
the neighbom’hood of the pole, and a great proportion of the fainter nebulae. No 
search has been made for new nebulae ; very many, however, have been found accidentally 
in the immediate neighbourhood of known nebulae, but for the most part they were 
faint objects presenting no features of interest. In every case where any peculiarity was 
detected, as for instance the convolution of a spiral, dark lines, or dark spaces, a rough 
sketch was made, and the more remarkable objects were selected for examination on 
favom’able nights, when the details were carefully filled in, sometimes with the aid of 
the micrometer. The veiy faint objects, and even the brighter, where there was a 
simple gradation of colour and no peculiarity of form, after having been examined on 
a tolerably good night, were rarely examined again. In our ever-varying climate, when 
we employ high powers and large apertures, vision is impeded more or less by the 
unsteadiness of the air ; it is impeded also by haze ; and in both respects the condition 
of the air varies immensely from night to night, and from hour to hour. The speculum 
also is not uniform in its action. With such sudden alternations of temperature, in a 
moist climate, it is frequently dewed, and gradually tarnishes. Artificially heating it 
would be a remedy ; but it would be an objectionable one, and we have not employed it. 
From all these causes we can scarcely say that any one object has been examined under 
a combination of favourable circumstances ; still it is not now probable that with the 
present instrument any remarkable additions will be made to the details of nebulse 
already carefully sketched, except in very favourable states of the atmosphere. Occasion- 
ally the air is so transparent and so steady, that magnifying power may be pushed very 
far ; and then, perhaps, something new comes out. Such opportunities, however, are rare ; 
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