The result is that no trace of " fiddling " exists, and the movable and fixed webs come sharply together in focus with the highest powers.
It didn't spin webs and looked more to Evelyn like a mutated cat, but the moment she recalled Kiera's fear, she also realized that the cat-like creature would easily pass as a large spider.
One of the most essential points in a good micrometer is that all the webs shall be so nearly in the same plane as to be well in focus together under the highest powers used, and at the same time absolutely free from " fiddling."
To avoid such error Dawes used double wires, not spider webs, placing the image of the star symmetrically between these wires, as in fig.
Other astronomers use the two distance-measuring webs, placed at a convenient distance apart, for position wires.
I, 2 and 3), used to bolt the head of one of the screws, and the instrument was provided with a slipping piece, giving motion to the micrometer by screws acting on two slides, one in right ascension, the other in declination, so that " either of the, webs can be placed upon either component of a double star with ease and certainty (Mem.
But in OS measures index error can be eliminated by bisecting both stars with the same web (or different webs of known interval fixed on the same frame), and not employing the fixed web at all.
The five fixed webs are attached to the table which is secured to the bottom of the box by the screws p. The three movable webs are attached to the projections XX on the frame aa.
These furrows have apparently been cut in situ with a very accurate engine; for not the slightest departure from parallelism can be detected in any of the movable webs relative to the fixed webs.
The varnish to fix the webs is applied, not on the surface T as is usual, but on a bevel for the purpose,' the position of the webs depending on their tension to keep them in their furrows.
A convenient feature in Repsolds' micrometer that the webs are very near the inner surface of the top of the box, so that the eye is not brought inconveniently close to the plate when high powers are used.
Da and The micrometer box, and of course with it the whole system of spider webs, is moved by the screw s, whilst the measuring web is independently moved by the screw S.
The electric lamp a gives illumination of the webs in a dark field, nearly in the manner described for the Cape transit circle micrometer; the intensity of illumination is regulated by a carbon-resistance controlled by the screw b.
Micrometers used for subdividing the spaces on graduated circles and scales have, in general, only a single pair of cross-webs or parallel webs moved by a single screw.
In all modern reading micrometers the cross webs of fig.
If the reading for coincidence of the movable with the fixed webs is known, we then obtain from the single reading of S the difference from coincidence of the divisions of the two scales.
X 5 mm., the sides of this square being parallel spider webs 4" of arc apart; the size of the square is reckoned from centre to centre of these double webs.
Webs serve not only for pointing on stars to determine their coordinates (in manner afterwards described), but also for estimating the diameters of the star-images in terms of these 4" intervals.
The webs of each set of movable webs shall, inter se, be strictly parallel, and the two sets shall be strictly at right angles to each other.
The double webs composing the sides of the fixed square shall be strictly parallel, and shall form a true square of exactly ten revolutions of the screw on the side.
The micrometer readings for coincidence of the movable webs with the webs of the fixed square shall be exactly 0 000R and io-000R.
The image of a normal reseau-square, as viewed in the microscope, shall exactly coincide with the square formed by the fixed webs - that is to say, the image of the sides of a normal reseau-square shall measure exactly io screw-revolutions.
By means of the quick rack motions A and B move the plate so as to bring the reseau-square into the centre of the field of the micrometer; then, by means of the screw heads o, p, perfect the coincidence of the " fixed square " of webs, with the image of the reseau-square.
By means of one of the micrometer screws X place the star's image in the middle of the six parallel webs which are moved by X.
Similarly, place the star's image in the middle of the webs moved by Y.
Vogel and his successors employed one or other form of measuring machine, provided with a microscope having single or close parallel webs which could be successively pointed on the photographed lines of the star spectrum and the lines of the terrestrial spectrum.
In the members of the typical genus Lemur, as well as in the allied Hapalemur and Lepidolemur, none of the toes or fingers are connected by webs, and all have the hind-limbs of moderate length, and the tail long.
The revolving masses are truly balanced by balance weights placed between ' the spokes of the wheels, or sometimes by prolonging the crank-webs and forming the prolongation into balance weights.
These webs, which are typically subcircular in form, consist of a system of threads radiating from a common centre and crossed at intervals, and approximately at right angles, by a series of concentric lines, the whole being suspended in a triangular, quadrangular or polygonal framework formed of so-called foundation lines, attached to the branches or leaves of trees or other firm objects in the neighbourhood.
Perfect orbicular webs are made by many genera of Argyopidae (Zilla, Meta, Gasteracantha), the best-known example being that of the common garden spider of England, Aranea or Epeira diademata; but these webs are not associated with any tubular retreat except such as are made under an adjoining leaf or in some nook hard by.
It was formerly supposed that this custom was peculiar to a single species, which was called the "gossamer" spider from the fact that the floating webs, when brought to the earth by rain or intercepted by bushes and trees, coat the foliage or grass with a sheeting of gossamer-like silk; but the habit is now known to be practised by the newly-hatched young of a great variety of species belonging to several distinct families.
Two genera of Argyopidae (Hyptiotes and Theridiosoma) construct spring-nets out of their incomplete webs of the orbicular type.
Males of the Argyopidae hang on the outskirt s of the webs of the females and signal their presence to her by jerking the radial threads in a peculiar manner.
Sometimes the shape of the spider combines with the colour to produce the same effect, as in the species of Uloborus, which as they hang in thin shabby-looking webs exactly resemble fragments of wind-blown rubbish.
The fore-limbs have four toes and a rudimentary thumb, all with claws; the hind limbs are larger, with five distinct toes, united by short webs at their bases.
For an account of the courtship and dancing of spiders, of their webs and floating lines, the reader is referred to the works of M'Cook (30) and the Peckhams (31), whilst an excellent account of the nests of trap-door spiders is given by Moggridge (32).
The genus Machaeropterus, consisting of four species, is very remarkable for the extraordinary form of some of the secondary wingfeathers in the males, in which the shaft is thickened and the webs changed in shape, as described and illustrated by P. L.
One fixed pair of webs is attached to the micrometer-box, the other pair is moved by the screw S.
It was he who compared laws to spiders' webs, which catch small flies and allow bigger ones to escape.
The two centre tail feathers attain a length of 34 in., and, being destitute of webs, have a thin wire-like appearance.
In the red bird of paradise (Paradisea rubra) the same feathers are greatly elongated and destitute of webs, but differ from those in the other species, in being flattened out like ribbons.
Itl ' At first girders had soli or plate webs, but for spans o 9 over ioo ft.
It was soon found that with plate webs the ratio of depth to span could not be economically increased beyond to T I T.
- In the case of girders with braced webs, the tension bars of which are not adapted to resist a thrust, another circumstance due to the position of the live load must be considered.
The Embiidae live in warm countries, and are very retiring in their habits, hiding under stones where they spin webs formed of silk produced by glands in the basal segments of the fore-feet.