ARTIFICIAL LIGHT LAMPS. 155 



of objects, for the examination of which good daylight is not to 

 be preferred to any other kind of light ; but good lamplight is 

 preferable to bad daylight. When daylight is employed, the 

 Microscope should be placed near a window, whose aspect should 

 be (as nearly as may be convenient) opposite to the side on which 

 the sun is shining; for the light of the sun reflected from a 

 bright cloud, is that which the experienced Microscopist will 

 almost always prefer, the rays proceeding from a cloudless blue 

 sky being by no means so well fitted for his purpose, and the 

 dull lurid reflection of a dark cloud being the worst of all. The 

 direct rays of the sun are far too powerful to be used with ad- 

 vantage, unless its intensity be moderated, either by reflection 

 from a plaster-of-paris or some other " white-cloud" mirror ( 58), 

 or by passage through some imperfectly transparent medium. 

 The moderator contrived by Mr. Eainey for lamp or gas-light 

 ( 75), has been found to answer equally well for direct sun- 

 light ; the glare and heating power of which it so effectually sub- 

 dues, as to destroy all tendency to injure the most delicate ob- 

 ject, or to confuse the observer's view of it ; whilst an illumina- 

 tion is obtained by its means, whose intensity renders it superior 

 for certain purposes to anything else. The young Microscopist 

 is earnestly recommended to make as much use of daylight as 

 possible ; not only because, in a large number of cases, the view 

 of the object which it affords is more satisfactory than that which 

 can be obtained by any kind of lamp-light, but also because it is 

 much less " trying" to the eyes. So great, indeed, is the dif- 

 ference between the two in this respect, that there are many 

 who find themselves unable to carry on their observations for 

 any length of time by lamp-light, although they experience 

 neither fatigue nor strain from many hours' continuous work by 

 daylight. 



75. When recourse is had to Artificial light, it is of great im- 

 portance, not only that it should be of good quality, but that the 

 arrangement for furnishing it should be suitable to the special 

 wants of the Microscopist. Thus, although a wax or composi- 

 tion candle affords a very pure light, yet its use is attended with 

 two inconveniences, which render its use very undesirable when 

 any better light can be obtained ; namely, the constant flicker- 

 ing of the flame, which is not sufficiently prevented by surround- 

 ing it with a chimney; and the continual alteration in its level, 

 which is occasioned by the consumption of the candle. The 

 most useful light for ordinary use, is that furnished by the steady 

 and constant flame of the lamp, fed either with oil, camphine, or 

 gas; the wick or burner should be cylindrical or " argand;" it 

 should be capable of adjustment to any height above the table ; 

 and a movable shade should be provided, by which the light may 

 be prevented from coming direct to the observer's eyes, or from 

 diffusing itself too widely through the room. These requisites 

 are supplied by the lamp commonly known as the " University" 



