HAllDWICKE'S SCIENCE-GOSSIP. 



63 



adopted, and, secondly, from difficulty of fiuding 

 au object registered by differeut observers and 

 "finders," arising from sliglit errors in the Einder 

 itself, and also from the various methods of 

 registration adopted by different observers. Mr. 

 W. K. Bridgeman, president of the Norfolk 

 and Norwich Microscopical Societj', has sug- 

 gested a plan which, by the aid of a very simple 

 piece of apparatus, obviates, to a very considerable 

 extent, the above-named objections to the Tinder. 

 He inserts in the eyepiece over the diaphragm' an 

 "indicator." This can be made in the following 

 manner : Unscrew the top of the eyepiece, so as to 

 expose the diaphragm ; cut a piece of card to fit 

 firmly over it ; draw a line across the diameter of the 

 disk of card, and cut an aperture in it of the same 

 size as that in tlie diiiphragm ; cut a little notch in 

 the ring in the same direction as the line, and gum 

 a line bristle in it, the point reaching nearly to the 

 centre ; when dry, phce in the eyepiece (close to the 

 diaphragm) and scre\y in the eye lens, and the indica- 

 tor is ready for use. Finders are only necessary when 

 the object is minute, or very rare on the slide, and the 

 higher powers are used. One of the squares in Malt- 

 wood's finder usually fills the whole of the field of a ^ 

 objective ; and if it so happened that au object always 

 occupied the same position as a square, no great 

 difficulty would be found in the registration of its 

 position ; but it more frequently occurs that portions 

 of squares only are in the field ; as for example, — 



?» 



or 



111 



1|2- 



"When this is the case, the indi- 



cator will be found of the greatest use. Bring the 

 object to be registered close to the point of the 

 bristle, remove the slide, and put (he Dnder in 

 its place, and note the exact position of the 

 point. We will suppose that the figures are 



the dot representing the point of the indi- 



the position of the object must then be 

 1 



cator 

 registered thus : 



-] ., the dot always representing 



the exact position of the object when in the centre 

 of the field. The rule for notation is that the 

 square on which the pointer rests is that which 

 must be written down. The error existing be- 

 tween two finders may be detected and remedied 

 in the following manner : Place the finder on the 

 stage, and bring the centre square into view, which 



would appear thus 



25 



remove it and put an 



ordinary glass slide in its place ; make a small per- 

 foration in a gummed label ; moisten it, and slip it 

 on the slide, so that the aperture is central. The 

 slide thus prepared can then be sent with the slides 

 requiring examination ; the second observer will 

 then test his own finder by the slide, and the error, 

 if any, noted. I have tried the plan proposed by 

 Mr. Bridgeman, and find that it answers admirably. 



One or two slight improvements may perhaps be 

 made — a ring of thin brass might be substituted for 

 card, and a small brass pin soldered into it for the 

 purpose of removing it from the eyepiece when re- 

 quired, and in place of the bristle, a piece of fine 

 spun glass will be found preferable ; indeed, so slight 

 a portion of the field is occupied by it, that the in- 

 dicator may always remain in the eyepiece, and will 

 be found useful in calling another observer's atten- 

 tion to any object, or part of an object, that may bo 

 desired. The test slide may be made a more per- 

 manent record by marking the centre with a small 

 ink-dot, and when dry, ruling (with a diamond) two 

 lines at right angles to each other across the dot ; 

 the point of intersection will then be found in the 

 centre of the field. — F. Kitton. 



A New Goniojieter Eyepiece. — Dr. Porter 

 and Mr. J. P. Southworth have succeeded in mak- 

 ing an eyepiece micro neter and goniometer, which 

 they say, equal in cheapness and accuracy, and are 

 much cheaper, than any yet seen. The objection to 

 the eyepiece micrometer in use is the lack of bold- 

 ness in tbe division lines, which makes them faint, 

 and hurtful to the eyes. To overcome this objection, 

 they have been led to make micrometers by the aid 

 of photography, and have succeeded. The advan- 

 tages of their goniometers over that ordinarily in 

 use, is, that the angles of the crystal and the degrees 

 of the goniometer are on the same line of sight 

 within the tube of the microscope, while in the 

 ordinary goniometer the degrees are marked outside 

 the tube. The photographic processes by means of 

 which this is achieved are not new, but may be 

 learned in any work on that subject. 



B T A 2^ Y. 



Ranunculxts PiCAUiA, L.— A common name for 

 this species sometimes met with in our Ploras is 

 " Lesser Celandine." This is a deceptive and con- 

 fusing name ; it is really a corruption of CIielidGiiium, 

 and the name of celandine should with propriety 

 only be applied to Chelidonium majus. The true 

 English name for this plant is Pllewort. Every one 

 who observes the " little things of nature" must have 

 noticed the peculiar whitening of the glossy golden 

 petals after they have been fully expanded about 

 fourteen days. Sometimes they appear with only 

 white patches in different parts of the petals ; at 

 others, it commences at the tip, and runs half or 

 two-thirds down the petals. Underneath the white 

 patch appears as if the cellular matter was in a 

 state of decay. The corolla is not marcescent, as 

 in the Campanulas (Bellflowers). The term marces- 

 cent cannot be applied to a deciduous corolla, and 

 without doubt the petals of the Pilewort are 

 deciduous. I am nut aware that any satisfactory 



