III. AIISCELLANEOUS. 617 



It can be used on shore with artificial horizon, in obtaining altitudes near 

 the zenith ; also as two single sextants, one of which can be used in case of 

 the other being damaged ; or one can be used by an assistant, and the other 

 retained by the observer. 



It can measure angles of nearly double the arc which can be measured by 

 the ordinary sextant. 



It can be used for the simultaneous measurement of two homogeneous 

 angles. 



For laying out curves for railways and harbours, it is invaluable to the 

 civil engineer and marine surveyor. 



3032. Universal Tripod Stand, an instrument for travellers. 



May be used for five instruments, viz.: 

 Sextant (for Lunars). 

 Telescope. 

 Barometer. 

 Prismatic compass. 

 Artificial horizon. 



3033. Large Double Sextant (6 in. radius) for taking two 

 lunars simultaneously ; an instrument for travellers. 



3033a. Capt. George's Improved Double box Sextant. 



Henry Porter. 



This instrument enables the observer to take right and left angles simul- 

 taneously, thus combining rapidity of use with great portability. 



3O33b. Box Sextant with improvement of wheel head to 

 telescope, and case. Henry Porter. 



3034. Pocket Compass, for bearing of objects, &c., an in- 

 strument for travellers. 0. S. Bishop. 



A combination of the ordinary compass and the dipping needle. The 

 advantage aimed at is, that it will act at or near the magnetic pole when the 

 ordinary compass ceases to be of any use. 



3035. The Inclined Reflecting Horizon, an instrument 



foi\ travellers. If. Porter. 



This instrument is used with the usual artificial horizon, to which it may 

 be said to form an appendage or adjunct. By its aid such increased power is 

 given to the sextant and artificial horizon that altitudes of the heavenly 

 bodies can be measured from the zenith to 30 below it, and also altitudes 

 from the horizon to 30 above it and 30 below it ; this the sextant and 

 artificial horizon have hitherto failed to do. It consists of a glass reflector, 

 supported by a framework, which has its underside ground mathematically 

 level, and this side floats on the surface of the mercury, carrying the reflector 

 at an angle of about 30 with the natural horizon, and when properly made 

 will always float on the mercury at the same angle ; it has been tested by 

 numerous observations, with satisfactory results. See observations and 

 drawings. 



