In 1998 and 1999 the Whipple Observatory 10 m telescope was used to search for diffuse gamma ray emission from the Galactic Plane .
At this time , the telescope was equipped with a large ( 4.8 ^ { o } ) field of view camera , well suited to detect diffuse \gamma -ray emission .
No signifiant evidence of emission was found .
Assuming the TeV emission profile matches EGRET observations above 1 GeV with a differential spectral index of 2.4 , we derive an upper limit of { 3.0 \cdot 10 ^ { -8 } \ > cm ^ { -2 } \ > s ^ { -1 } \ > sr ^ { -1 } } for the average diffuse emission above 500 ~ { } GeV in the galactic latitude range from -2 ^ { o } to +2 ^ { o } at galactic longitude 40 ^ { o } .
Comparisons with EGRET observations provide a lower limit of 2.31 for the differential spectral index of the diffuse emission , assuming there is no break in the spectrum between 30 GeV and 500 GeV .
This constrains models for diffuse emission with a significant inverse Compton contribution .