TECHNOLOGICAL REPOSITORY;

OR,

DISCOVERIES AND IMPROVEMENTS

IN THE

Useful Arts,

BEING A CONTINUATION OF HIS TECHNICAL REPOSITORY.

BY THOMAS GILL, Patent-Agent,

AND DEMONSTRATOR IN TECHNOLOGY, ON THE APPLICATION OF
SCIENCE TO THE USEFUL ARTS AND MANUFACTURES;
UPWARDS OF TWENTY YEARS A CHAIRMAN OF THE COMMITTEE OF MECHANICS IN THE
SOCIETY FOR THE ENCOURAGEMENT OF ARTS, MANUFACTURES,

AND COMMERCE, ADELPHI, LONDON;

HONORARY MEMBER OF THE ROYAL PRUSSIAN ECONOMICAL SOCIETY OF POTSDAM; AND
A CORRESPONDING MEMBER OF THE ROYAL BAVARIAN POLYTECHNICAL
AND AGRICULTURAL SOCIETIES OF MUNICH.

VOL. III.

LONDON:

PRINTED BY W. SPIERS,

399, OXFORD-STREET;

EDITED AT GILL'S PATENT AGENCY & COMMISSION OFFICE,

125. STRAND, OPPOSITE EXETER 'CHANGE;

PUBLISHED BY THOMAS HURST, EDWARD CHANCE, AND COMPANY,

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1829.

GILL'S

TECHNOLOGICAL REPOSITORY.

I.-On the Microscope. By the EDITOR.

WITH PLATES.

(Continued from vol. II. page 230.)

On the Cynips of the Oak.-On a visit which the Editor recently paid to Mr. T. Carpenter, after he had illustrated his observations respecting the aphides, contained in a subsequent article in the present number, by various interesting specimens placed under his microscope, he exhibited under that instrument, as opaque objects, variety of splendid flies of the genus cynips, usually termed gall-flies, from their attacks upon the trees producing those galls or excrescences which are so frequently found on them; he proceeded to give him the history of those various species which produce the oak-apples, and the curious bunches of a moss-like appearance on the dog-rose trees, illustrating the subject as he proceeded by the sight of numerous specimens which he had preserved, in order to prove the facts he stated. He began with that of the oakapple, showing him the instrument at the end of its abdomen, with which it perforates the bud in its early state, and deposits its eggs within it. The tree being thus wounded in that part, and probably a poisonous juice being also injected at the same time, causes the sap, as it flows to that part, to stop; and, instead of the bud expanding into a branch, an excrescence or swelling is formed, being indeed what is termed the oak-apple; within this, the eggs

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