The invention particularly relates to a clinometer for measuring the angle of elevation of an object, to enable calculation of the height of an object at a known distance or the distance of an object of known height.

A conventional clinometer as used professionally in surveying (also known as an"Indian Clinometer") comprises a solid base fitted with a levelling screw mechanism and having an arm pivoted at each of its ends, and adapted to be moved upright in use. One arm is short and has a peephole. The other arm is longer and has a central slot, which carries a scale calibrated in degrees or in natural tangents. Within the slot can be viewed a slide, having a cross-hair for sighting an object. The slide has a rack and pinion drive for moving it up and down the longer upright arm. When the Indian clinometer has been set up with the base level and aligned as desired, a view is taken through the peephole and the rack and pinion mechanism is used to adjust the slide until the cross-hair coincides with the object to be measured. The position of the slide is read off the scale and the angle of inclination is then known. Calculations can be made to establish the height of the object viewed or its distance from the observer according to geometric principles.

In order to teach such principles, it would be desirable to provide an educational apparatus or toy which can be used more easily than a conventional Indian clinometer and which is robust and self-contained.

According to the invention there is provided an educational toy clinometer apparatus, which comprises a body adapted to be hand held, for example, having a hand grip, the body defining a viewing path having an eyepiece for viewing a distant object, a protractor scale freely rotatably mounted to the body and gravitationally biassed to hang in a given orientation, a pointer fixed relative to the body and adapted to cooperate with the protractor scale to indicate a value to be read off, and a reflector in or adjacent said viewing path adapted to reflect said pointer and said indicated value to the eyepiece.

The body may comprise a closed housing.

A tunnel may be provided through the housing to afford said viewing path and optionally lenses may be provided on the eyepiece and at the objective end of the viewing path.

The housing may have a lateral enlargement to house said reflector adjacent the viewing path. The reflector is preferably a mirror.

The housing may have a window adjacent the protractor. In a preferred form the protractor may be transparent and the pointer may lie on the side of the protractor remote from the window. The window may also have a lens.

The pointer may have twin points, one of which acts as an indicator on the protractor scale and the other of which acts as a reference pointer to be aligned with the object to be viewed.

Alternatively, the objective lens may have a cross-hair for alignment with the object to be viewed.

An embodiment of the invention will now be described in more detail by way of example only, with reference to the accompanying drawing in which:- FIGURE 1 is a diagrammatic illustration of the way in which a clinometer may be used; FIGURE 2 is an exploded perspective view of an educational or toy clinometer apparatus embodying the invention; FIGURE 3 is an optional detail of a pointer of the apparatus shown in Figure 2.

Referring to Figure 1, a person 10 can use a clinometer to measure the angle of inclination between the position of his or her eye and a selected point on a distant object, for instance the top of a tree 11. The angle of inclination can then be used, in combination with other measurements such as the distance 12 between the person 10 and the tree 11 and the height 13 to eye level of the person 10, to make a calculation of the height 14 of the tree. Conversely, if the height of a viewed object is known, for instance the height of a mountain, the distance away can be calculated, using the principles of geometry.

An embodiment of educational or toy clinometer apparatus is shown in Figure 2 and comprises a hand-held body 15 in the form of a disk-shaped housing 16 having a handle 17. One side of the housing is defined by a back-plate 18 which is secured in place. The back-plate 18 has a lateral enlargement 19, but otherwise defines a tunnel viewing path 20 having an eyepiece 21 with an optional eyepiece lens 22 and an optional objective lens 23.

An axle pin 24 is fixed within the housing 16 and a protractor 25 having a scale 26 marked in degrees is freely rotatably mounted on the axle pin 24. Suitable lubricant such as silicone grease may be used to ensure free rotation. The protractor has a cut-out 27 to ensure that it always hangs in the same orientation under gravitational bias.

A pointer plate 28 is fixed in the housing 16, mounted coaxially with the protractor on the axle pin, but non-rotatable. The pointer plate 28 has an aperture 29 having a pointer 30 which cooperates with the scale 26 to indicate a value. The housing may be transparent, but is preferably not, in this case being provided with a window 31, optionally having a lens 32, to illuminate the protractor, which is of transparent or translucent material.

A reflector in the form of a mirror 33 is mounted in the lateral enlargement 19 of the tunnel viewing path 20. Alternatively, the reflector could be a prism.

In use, the body 15 is held by the handle 17 and raised to the eye, so that the observer can see a distant object through the viewing path 20. At the same time, the observer can see, reflected in the reflector 33, the value of angle of inclination indicated on the scale 26 of the protractor 25 by the pointer 30 of the pointer plate 28. In order to pinpoint the viewed object more exactly, there may be a cross-hair in the objective lens 23 or the pointer plate 28 may have twin pointers 30,30a, as shown in Figure 3.

The educational apparatus or toy will be capable of measuring the angle of inclination of a viewed object in a simple and direct fashion, with reasonable accuracy. It is robust and self-contained. Where all three of the optional lenses are provided, the body can be fully sealed to avoid internal damage or tampering.