An object reference is required for the non-static field, method, or property 'GameBase.Asset'

I need to spawn up to 81 entities of one type. The entity has several properties like weight and colour. So I created a new class “Sphere” and planned to load the asset and add it to “Entities” in the constructor. However, this throws an error:

An object reference is required for the non-static field, method, or property ‘GameBase.Asset’

public class Sphere
{
    Entity Entity { get; set; }
    int weight { get; set; }

    public Sphere()
    {
        this.Entity = Asset.Load<Entity>("sphereEntity");
        Entities.Add(this.Entity);
    }
}

Any ideas how to solve this?

Sphere have to be Script Context to have Entities in it.