The Holcombe Mount

from Reflecting Telescopes

by H. L. Smith

from a column in Annals of Science, 1853


[Mel Bartels' introductory comments] The Holcombe mount stands as a remarkable achievement in design, anticipating modern design principles a century earlier. Holcombe's mount is simple, sturdy, with unexpectedly large aperture for its era. He eschewed tracking for the compelling task of visually revealing the heavens. There are remarkable similarities to John Dobson's design that came more than a century later. Holcombe also began this country's first telescope making company at a time when it was thought that Americans were not up to the task. When Alvan Clark began his ground breaking optics work, he visited Holcombe and purchased glass from him. Holcombe’s mount lives on today in the guise of F.J.Seller’s mount. America's oldest surviving observatory began with a Holcombe telescope, eventually to be replaced with a Clark refractor decades later, the task of re-polishing and figuring the speculum mirror proving too burdensome. A great image is at http://learninglab.si.edu/q/r/12225


The stand for the reflecting telescope invented by Mr. Holcombe is undoubtedly the most economical and efficient ever made. Below is represented the general appearance of the telescope and stand.




The lower end of the telescope, where the speculum is located at 'a', rests upon the ground; the upper end, which is somewhat larger, in order that the head my not obstruct the light, when the eye is applied at 'b', is supported by two sliding legs 'c', and 'd', which are lengthened or shortened by means of the thumb-pins 'e', 'f', shown more plainly in fig.2; a catgut cord passes from the thumb-pins down the front of the upper sliding rod, over a small pulley at 'g' and 'h', thence along a groove cut in the front surface of the lower sliding rod up to nearly its top at 'c' and 'd', where it is fastened; an iron hand attached to the top of the lower rod, and another attached to the bottom of the upper rod, holds the whole firmly, yet allows a free movement when they are made to slide upon each other by winding or unwinding the cat-gut cord upon the barrel of the thumb-pins 'e' and 'f'. The lower ends of the sliding rods are pointed and armed with iron, and at the lower end of the upper part of the sliding rods, camping screws are placed, just below the pulleys in order that the whole may be securely fastened while being transported from place to place. The method of attachment to the upper end of the tube is shown in fig. 2, a brass saddle 'i', is bolted to the tube, between the ears of which the parallel plates of brass 'k', 'l', move freely upon the pin 'm' 'n', between these plates of brass, the sliding legs are placed, and turn upon the two pins 'o', 'p'. It will be perceived, that by extending the sliding legs at the bottom, or by lengthening or shortening them, almost any required altitude may be given to the telescope, and to keep the thumb-pins 'e' and 'r', from unwinding with the weight of the telescope, two pieces of hard wood 'r', and 's', are located below them, having a steadying pin at the bottom and a clamping screw at the top as shown in fig. 2, by turning this clamping screw the smooth flange of the thumb-pins is pinched between the rod and bit of wood, and thus any requisite amount of friction is obtained. The eye-piece is located at 'b', fig. 1, and screws or slips into a ring attached to a bar, which is racked, and the proper position for distinct vision is obtained by means of the milled head. The finder 'u' is a small telescope mounted upon two pins, which pass through elongated holes in the tube, and by means of nuts which screw upon the pins outside and inside of the tube, is held firmly, and adjusted, so that when any object is brought upon the intersection of the hairs in the focus of the eye-piece, it will be in the field of view in the telescope. The stand I have now described is remarkably steady, since the speculum, which forms the image, rests upon the ground.






from:
Annals of Science, Volume 1, page 141 (April 15, 1853),
found in 23 libraries in the USA,
being a record of inventions and improvements in applied science,
Publication: Cleveland, Printed by Harris and Fairbanks.
Vol. 1 "including the transactions of the American association for the advancement of science." Ceased with 1854
Vol. 2, "including the transactions of the Cleveland academy of natural sciences.", American association for the advancement of science, Cleveland academy of natural science.
Responsibility: Conducted by Hamilton L. Smith.

scanned by Matt Considine, transcribed by Mel Bartels.

Also see Sky and Telescope magazine, August 1978, page 158

For more on F.J.Seller's mount and modern variations, see August 1976 Sky and Telescope, pages 138-140.

A recent Holcombe, nicely done is at http://www.cloudynights.com/topic/491231-a-long-focus-newt-on-a-holcomb-mounting/

For more on the remarkable Holcombe, the first American manufacturer of telescopes, see http://en.wikipedia.org/wiki/Amasa_Holcomb and http://www.europa.com/~telscope/holcomb.txt